%0 Conference Proceedings
%B 10th International Workshop on Scalable Semantic Web Knowledge Base Systems
%D 2014
%T Distributed OWL EL Reasoning: The Story So Far
%A Raghava Mutharaju
%A Pascal Hitzler
%A Prabhaker Mateti
%E Thomas Liebig
%E Achille Fokoue
%K classification
%K distributed reasoning
%K MapReduce
%K OWL 2 EL
%K peer-to-peer system
%X Automated generation of axioms from streaming data, such as traffic and text, can result in very large ontologies that single machine reasoners cannot handle. Reasoning with large ontologies requires distributed solutions. Scalable reasoning techniques for RDFS, OWL Horst and OWL 2 RL now exist. For OWL 2 EL, several distributed reasoning approaches have been tried, but are all perceived to be inefficient. We analyze this perception. We analyze completion rule based distributed approaches, using different characteristics, such as dependency among the rules, implementation optimizations, how axioms and rules are distributed. We also present a distributed queue approach for the classification of ontologies in description logic EL+(fragment of OWL 2 EL).
%B 10th International Workshop on Scalable Semantic Web Knowledge Base Systems
%I CEUR
%C Riva del Garda, Italy
%V 1261
%P 61-76
%8 10/2014
%G eng
%0 Conference Paper
%B 2013 IEEE/WIC/ACM International Conference on Web Intelligence
%D 2013
%T Automatic Domain Identification for Linked Open Data
%A Sarasi Lalithsena
%A Prateek Jain
%A Pascal Hitzler
%A Amit Sheth
%K Dataset search
%K Domain Identification
%K Linked Open Data Cloud
%X Linked Open Data (LOD) has emerged as one of the largest collections of interlinked structured datasets on the Web. Although the adoption of such datasets for applications is increasing, identifying relevant datasets for a specific task or topic is still challenging. As an initial step to make such identification easier, we provide an approach to automatically identify the topic domains of given datasets. Our method utilizes existing knowledge sources, more specifically Freebase, and we present an evaluation which validates the topic domains we can identify with our system. Furthermore, we evaluate the effectiveness of identified topic domains for the purpose of finding relevant datasets, thus showing that our approach improves reusability of LOD datasets.
%B 2013 IEEE/WIC/ACM International Conference on Web Intelligence
%I ACM
%C Atlanta, GA
%G eng
%1 Full citation
Sarasi Lalithsena, Prateek Jain, Pascal Hitzler, and Amit Sheth, "Automatic Domain Identification for Linked Open Data," 2013 IEEE/WIC/ACM International Joint Conferences on Web Intelligence (WI) and Intelligent Agent Technologies (IAT), Atlanta, GA, 2013, pp. 205-212.
doi: 10.1109/WI-IAT.2013.206
%0 Conference Paper
%B 10th Extended Semantic Web Conference (ESWC 2013 )
%D 2013
%T Logical Linked Data Compression
%A Amit Joshi
%A Pascal Hitzler
%A Guozhu Dong
%X Linked data has experienced accelerated growth in recent years. With the continuing proliferation of structured data, demand for RDF compression is becoming increasingly important. In this study, we introduce a novel lossless compression technique for RDF datasets, called Rule Based Compression (RB Compression) that compresses datasets by generating a set of new logical rules from the dataset and removing triples that can be inferred from these rules. Unlike other compression techniques, our approach not only takes advantage of syntactic verbosity and data redundancy but also utilizes semantic associations present in the RDF graph. Depending on the nature of the dataset, our system is able to prune more than 50% of the original triples without affecting data integrity.
%B 10th Extended Semantic Web Conference (ESWC 2013 )
%C Montpellier, France
%8 05/2013
%G eng
%0 Conference Proceedings
%B ODBASE 2012
%D 2012
%T Alignment-based Querying of Linked Open Data
%A Amit Krishna
%A Prateek Jain
%A Pascal Hitzler
%A Peter Z. Yeh
%A Kunal Verma
%A Amit Sheth
%A Mariana Damova
%X The Linked Open Data (LOD) cloud is rapidly becoming the largest interconnected source of structured data on diverse domains. The potential of the LOD cloud is enormous, ranging from solving challenging AI issues such as open domain question answering to automated knowledge discovery. However, due to an inherent distributed nature of LOD and a growing number of ontologies and vocabularies used in LOD datasets, querying over multiple datasets and retrieving LOD data remains a challenging task. In this paper, we propose a novel approach to querying linked data by using alignments for processing queries whose constituent data come from heterogeneous sources. We also report on our Alignment based Linked Open Data Querying System (ALOQUS) and present the architecture and associated methods. Using the state of the art alignment system BLOOMS, ALOQUS automatically maps concepts in users’ SPARQL queries, written in terms of a conceptual upper ontology or domain specific ontology, to different LOD concepts and datasets. It then creates a query plan, sends sub-queries to the different endpoints, crawls for co-referent URIs, merges the results and presents them to the user. We also compare the existing querying systems and demonstrate the added capabilities that the alignment based approach can provide for querying the Linked data.
%B ODBASE 2012
%C Rome, Italy
%V 7566
%P 807-824
%8 09/2012
%G eng
%0 Conference Paper
%B Workshop on GIScience in the Big Data Age, in conjunction with the 7th International Conference on Geographic Information Science 2012 (GIScience 2012)
%D 2012
%T Semantics and Ontologies for EarthCube
%A Gary Berg-Cross
%A Isabel Cruz
%A Mike Dean
%A Timothy Finin
%A Pascal Hitzler
%A Hook Hua
%A Mark Gahegan
%A Krzysztof Janowicz
%A Naicong Li
%A Philip Murphy
%A Bryce Nordgren
%A Leo Obrst
%A Mark Schildhauer
%A Amit Sheth
%A Krishna Sinha
%A Anne Thessen
%A Nancy Wiegand
%A Ilya Zaslavsky
%E Krzysztof Janowicz
%E Carsten Keßler
%E Tomi Kauppinen
%E Dave Kolas
%E Simon Scheider
%K Tractable Reasoning with Ontologies
%X Semantic technologies and ontologies play an increasing role in scientific workflow systems and knowledge infrastructures. While ontologies are mostly used for the semantic annotation of metadata, semantic technologies enable searching metadata catalogs beyond simple keywords, with some early evidence of semantics used for data translation. However, the next generation of distributed and interdisciplinary knowledge infrastructures will require capabilities beyond simple subsumption reasoning over subclass relations. In this work, we report from the EarthCube Semantics Community by highlighting which role semantics and ontologies should play in the EarthCube knowledge infrastructure. We target the interested domain scientist and, thus, introduce the value proposition of semantic technologies in a non-technical language. Finally, we commit ourselves to some guiding principles for the successful implementation and application of semantic technologies and ontologies within EarthCube.
%B Workshop on GIScience in the Big Data Age, in conjunction with the 7th International Conference on Geographic Information Science 2012 (GIScience 2012)
%C Columbus, OH
%P 11-16
%8 09/2012
%G eng
%0 Conference Paper
%B International World Wide Web Conference (WWW2011)
%D 2011
%T A Better Uncle For OWL - Nominal Schemas for Integrating Rules and Ontologies
%A Markus Krotzsch
%A Frederick Maier
%A Adila Alfa Krisnadhi
%A Pascal Hitzler
%K Datalog
%K Description Logic
%K Semantic Web Rule Language
%K SROIQ
%K tractability
%K Web Ontology Language
%X We propose a description-logic style extension of OWL 2 with nominal schemas which can be used like 'variable nominal classes' within axioms. This feature allows ontology languages to express arbitrary DL-safe rules (as expressible in SWRL or RIF) in their native syntax. We show that adding nominal schemas to OWL 2 does not increase the worst-case reasoning complexity, and we identify a novel tractable language SROELV_3(⊓, X) that is versatile enough to capture the lightweight languages OWL EL and OWL RL.
%B International World Wide Web Conference (WWW2011)
%I Proceedings of the 20th International World Wide Web Conference (WWW2011)
%C New York
%G eng
%0 Journal Article
%D 2011
%T Computing Inconsistency Measure based on Paraconsistent Semantics
%A Yue Ma
%A Guilin Qi
%A Pascal Hitzler
%X Measuring inconsistency in knowledge bases has been recognized as an important problem in several research areas. Many methods have been proposed to solve this problem and a main class of them is based on some kind of paraconsistent semantics. However, existing methods suffer from two limitations: (i) they are mostly restricted to propositional knowledge bases; (ii) very few of them discuss computational aspects of computing inconsistency measures. In this article, we try to solve these two limitations by exploring algorithms for computing an inconsistency measure of first-order knowledge bases. After introducing a four-valued semantics for first-order logic, we define an inconsistency measure of a first-order knowledge base, which is a sequence of inconsistency degrees. We then propose a precise algorithm to compute our inconsistency measure. We show that this algorithm reduces the computation of the inconsistency measure to classical satisfiability checking. This is done by introducing a new semantics, named S[n]-4 semantics, which can be calculated by invoking a classical SAT solver. Moreover, we show that this auxiliary semantics also gives a direct way to compute upper and lower bounds of inconsistency degrees. That is, it can be easily revised to compute approximating inconsistency measures. The approximating inconsistency measures converge to the precise values if enough resources are available. Finally, by some nice properties of the S[n]-4 semantics, we show that some upper and lower bounds can be computed in P-time, which says that the problem of computing these approximating inconsistency measures is tractable.
%G eng
%0 Conference Paper
%B 8th Extended Semantic Web Conference, ESWC 2011
%D 2011
%T Contextual Ontology Alignment of LOD With an Upper Ontology: A Case Study With Proton
%A Prateek Jain
%A Peter Z. Yeh
%A Kunal Verma
%A Reymonrod Vasquez
%A Mariana Damova
%A Pascal Hitzler
%A Amit Sheth
%K Contextual Ontology Alignment
%K Linked Open Data
%K Ontology Mapping
%K Schema Alignment
%X The Linked Open Data (LOD) is a major milestone towards realizing the Semantic Web vision, and can enable applications such as robust Question Answering (QA) systems that can answer queries requiring multiple, disparate information sources. However, realizing these applications requires relationships at both the schema and instance level, but currently the LOD only provides relationships for the latter. To address this limitation, we present a solution for automatically finding schema-level links between two LOD ontologies -- in the sense of ontology alignment. Our solution, called BLOOMS+, extends our previous solution (i.e. BLOOMS) in two significant ways. BLOOMS+ 1) uses a more sophisticated metric to determine which classes between two ontologies to align, and 2) considers contextual information to further support (or reject) an alignment. We present a comprehensive evaluation of our solution using schema-level mappings from LOD ontologies to Proton (an upper level ontology) -- created manually by human experts for a real world application called FactForge. We show that our solution performed well on this task. We also show that our solution significantly outperformed existing ontology alignment solutions (including our previously published work on BLOOMS) on this same task.
%B 8th Extended Semantic Web Conference, ESWC 2011
%I Proceedings of 8th Extended Semantic Web Conference, ESWC 2011
%C Greece
%G eng
%0 Conference Paper
%B The Semantic Web - ISWC 2011 - 10th International Semantic Web Conference, Bonn, Germany, October 23-27, 2011
%D 2011
%T Local Closed World Reasoning: Grounded Circumscription for OWL
%A Kunal Sengupta
%A Adila Alfa Krisnadhi
%A Pascal Hitzler
%X We present a new approach to adding closed world reasoning to the Web Ontology Language OWL. It transcends previous work on circumscriptive description logics which had the drawback of yielding an undecidable logic unless severe restrictions were imposed. In particular, it was not possible, in general, to apply local closure to roles. In this paper, we provide a new approach, called grounded circumscrip- tion, which is applicable to SROIQ and other description logics around OWL without these restrictions. We show that the resulting language is decidable, and we derive an upper complexity bound. We also provide a decision procedure in the form of a tableaux algorithm.
%B The Semantic Web - ISWC 2011 - 10th International Semantic Web Conference, Bonn, Germany, October 23-27, 2011
%I Proceedings, Part I. Lecture Notes in Computer Science Vol. 7031, Springer, Heidelberg, 2011
%C Bonn, Germany
%G eng
%0 Conference Paper
%B Web Reasoning and Rule Systems. 5th International Conference, RR 2011, Galway, Ireland, August 29-30, 2011
%D 2011
%T Local closed world semantics: grounded circumscription for description logics
%A Kunal Sengupta
%A Adila Alfa Krisnadhi
%A Pascal Hitzler
%K circumscription
%K Description Logic
%K local closed world
%X We present an improved local closed world extension for description logics. It is based on circumscription, and deviates from previous circumscriptive description logics [1,3] in that extensions of minimized predicates may contain only extensions of named individuals in the knowledge base. Besides an (arguably) higher intuitive appeal, the improved semantics is applicable to expressive description logics without loss of decidability.
%B Web Reasoning and Rule Systems. 5th International Conference, RR 2011, Galway, Ireland, August 29-30, 2011
%I Lecture Notes in Computer Science Vol. 6902, Springer, Heidelberg, 2011
%C Galway, Ireland
%G eng
%0 Conference Paper
%B Local Closed World Semantics: Keep it simple, stupid!
%D 2011
%T Local Closed World Semantics: Keep it simple, stupid!
%A Adila Alfa Krisnadhi
%A Kunal Sengupta
%A Pascal Hitzler
%K circumscription
%K closed world
%K decidability
%K Description Logic
%B Local Closed World Semantics: Keep it simple, stupid!
%G eng
%0 Journal Article
%D 2011
%T Local Closed-World Reasoning with Description Logics under the Well-founded Semantics
%A Matthias Knorr
%A Jose Julio Alferes
%A Pascal Hitzler
%K Description logics and ontologies
%K Knowledge Representation
%K logic programming
%K Non-monotonic reasoning
%K Semantic Web
%X An important question for the upcoming Semantic Web is how to best combine open world ontology languages, such as the OWL-based ones, with closed world rule-based languages. One of the most mature proposals for this combination is known as hybrid MKNF knowledge bases (Motik and Rosati, 2010 [52]), and it is based on an adaptation of the Stable Model Semantics to knowledge bases consisting of ontology axioms and rules. In this paper we propose a well-founded semantics for nondisjunctive hybrid MKNF knowledge bases that promises to provide better efficiency of reasoning, and that is compatible with both the OWL-based semantics and the traditional Well-Founded Semantics for logic programs. Moreover, our proposal allows for the detection of inconsistencies, possibly occurring in tightly integrated ontology axioms and rules, with only little additional effort. We also identify tractable fragments of the resulting language.
%G eng
%0 Conference Paper
%D 2011
%T Nominal Schemas for Integrating Rules and Description Logics
%A Markus Krotzsch
%A Frederick Maier
%A Adila Alfa Krisnadhi
%A Pascal Hitzler
%X We propose an extension of SROIQ with nominal schemas which can be used like Âvariable nominal conceptsÂ within axioms. This feature allows us to express arbitrary DL-safe rules in description logic syntax. We show that adding nominal schemas to SROIQ does not increase its worst-case reasoning complexity, and we identify a family of tractable DLs SROELVn that allow for restricted use of nominal schemas.
%G eng
%0 Generic
%D 2011
%T OWL and Rules
%A Adila Alfa Krisnadhi
%A Frederick Maier
%A Pascal Hitzler
%X The relationship between the Web Ontology Language OWL and rule-based formalisms has been the subject of many discussions and research investigations, some of them controversial. From the many attempts to reconcile the two paradigms, we present some of the newest developments. More precisely, we show which kind of rules can be modeled in the current version of OWL, and we show how OWL can be extended to incorporate rules without compromising OWL design principles.
%I Reasoning Web. Semantic Technologies for the Web of Data. 7th International Summer School 2011, Galway, Ireland, August 23-27, 2011
%G eng
%0 Conference Paper
%B Web Reasoning and Rule Systems. 5th International Conference, RR 2011, Galway, Ireland, August 29-30, 2011
%D 2011
%T Paraconsistent Semantics for Hybrid MKNF Knowledge Bases
%A Shasha Huang
%A Qingguo Li
%A Pascal Hitzler
%X Hybrid MKNF knowledge bases, originally based on the stable model semantics, is a mature method of combining rules and Description Logics (DLs). The well-founded semantics for such knowledge bases has been proposed subsequently for better efficiency of reasoning. However, integration of rules and DLs may give rise to inconsistencies, even if they are respectively consistent. Accordingly, reasoning systems based on the previous two semantics will break down. In this paper, we employ the four-valued logic proposed by Belnap, and present a paraconsistent semantics for Hybrid MKNF knowledge bases, which can detect inconsistencies and handle it effectively. Besides, we transform our proposed semantics to the stable model semantics via a linear transformation operator, which indicates that the data complexity in our paradigm is not higher than that of classical reasoning. Moreover, we provide a fixpoint algorithm for computing paraconsistent MKNF models.
%B Web Reasoning and Rule Systems. 5th International Conference, RR 2011, Galway, Ireland, August 29-30, 2011
%I Proceedings. Lecture Notes in Computer Science Vol. 6902, Springer, Heidelberg, 2011
%C Galway, Ireland
%G eng
%0 Generic
%D 2011
%T Reconciling OWL and Rules
%A David Carral Martinez
%A Adila Alfa Krisnadhi
%A Frederick Maier
%A Kunal Sengupta
%A Pascal Hitzler
%K OWL and description logic and decidability and local closed world and reasoningalgorithms and rules and datalog
%X We report on a recent advance in integrating Rules and OWL. We discuss a recent proposal, known as nominal schemas, which realizes a seamless integration of Datalog rules into the description logic SROIQ which underlies OWL 2 DL. We present extensions of the standardized OWL syntaxes to incorporate nominal schemas, reasoning algorithms, and a rst naive implementation. And we argue why this approach goes a long way towards overcoming the present paradigm split.
%G eng
%0 Conference Paper
%B 8th International Workshop on OWL: Experiences and Directions (OWLED 2011)
%D 2011
%T Representation of Parsimonious Covering Theory in OWL-DL
%A Cory Henson
%A Krishnaprasad Thirunarayan
%A Amit Sheth
%A Pascal Hitzler
%K OWL and Abductive Reasoning and Parsimonious Covering Theory
%X The Web Ontology Language has not been designed for representing abductive inference, which is often required for applications such as medical disease diagnosis. As a consequence, existing OWL ontologies have limited ability to encode knowledge for such applications. In the last 150 years, many logic frameworks for the representation of abductive inference have been developed. Among these frameworks, Parsimonious Covering Theory (PCT) has achieved wide recognition. PCT is a formal model of diagnostic reasoning in which knowledge is represented as a network of causal associations, and whose goal is to account for observed symptoms with plausible explanatory hypotheses. In this paper, we argue that OWL does provide some of the expressivity required to approximate diagnostic reasoning, and outline a suitable encoding of PCT in OWL-DL.
%B 8th International Workshop on OWL: Experiences and Directions (OWLED 2011)
%C San Francisco, California
%G eng
%0 Journal Article
%D 2011
%T Semantic Web surveys and applications.
%A Krzysztof Janowicz
%A Pascal Hitzler
%P 65-66
%G eng
%0 Journal Article
%J Semantic Web – Interoperability, Usability, Applicability
%D 2011
%T Semantic Web Tools and Systems.
%A Pascal Hitzler
%A Krzysztof Janowicz
%X Semantic Web research relies on a number of key methodologies such as knowledge representation languages or reasoning algorithms. As a research community, however, we could not progress based on these methodologies exclusively, but require tools and systems that realize our research results as key technologies for the Semantic Web.
%B Semantic Web – Interoperability, Usability, Applicability
%I IOS Press
%P 1-2
%G eng
%0 Conference Paper
%B What's happening in Semantic Web ... and what FCA could have to do with it
%D 2011
%T What's happening in Semantic Web ... and what FCA could have to do with it.
%A Pascal Hitzler
%X The Semantic Web [27] is gaining momentum. Driven by over 10 years of focused project funding in the US and the EU, Semantic Web Technologies are now entering application areas in industry, academia, government, and the open Web. The Semantic Web is based on the idea of describing the meaning - or semantics - of data on the Web using metadata - data that describes other data - in the form of ontologies, which are represented using logic-based knowledge representation languages [26]. Central to the transfer of Semantic Web into practice is the Linked Open Data effort [7], which has already resulted in the publication, on the Web, of billions of pieces of information using ontology languages. This provides the basic data needed for establishing intelligent system applications on the Web in the tradition of Semantic Web Technologies.
%B What's happening in Semantic Web ... and what FCA could have to do with it
%I Lecture Notes in Artificial Intelligence 6628, Springer, Heidelberg
%C Formal Concept Analysis, 9th International Conference, ICFCA 2011, Nicosia, Cyprus, May 2011
%G eng
%0 Conference Paper
%D 2011
%T What's happening in Semantic Web ... and what FCA could have to do with it
%A Pascal Hitzler
%G eng
%0 Conference Paper
%B 21st International Conference, DEXA 2010
%D 2010
%T Approximate Instance Retrieval on Ontologies
%A Tuvshintur Tserendorj
%A Stephan Grimm
%A Pascal Hitzler
%X With the development of more expressive description logics(DLs) for the Web Ontology Language OWL the question arises how we can properly deal with the high computational complexity for efficient reasoning. In application cases that require scalable reasoning with expressive ontologies, non-standard reasoning solutions such as approximate reasoning are necessary to tackle the intractability of reasoning in expressive DLs. In this paper, we are concerned with the approximation of the reasoning task of instance retrieval on DL knowledge bases, trading correctness of retrieval results for gain of speed. We introduce our notion of an approximate concept extension and we provide implementations to compute an approximate answer for a concept query by a suitable mapping to efficient database operations. Furthermore, we report on experiments of our approach on instance retrieval with the Wine ontology and discuss first results in terms of error rate and speed-up.
%B 21st International Conference, DEXA 2010
%C Bilbao, Spain
%G eng
%0 Journal Article
%J International Journal of Software and Informatics
%D 2010
%T Computational Complexity and Anytime Algorithm for Inconsistency Measurement
%A Yue Ma
%A Guilin Qi
%A Guohui Xiao
%A Pascal Hitzler
%A Zuoquan Lin
%K algorithm
%K computational complexity
%K inconsistency measurement
%K multi-valued logic
%X Measuring inconsistency degrees of inconsistent knowledge bases is an important problem as it provides context information for facilitating inconsistency handling. Many methods have been proposed to solve this problem and a main class of them is based on some kind of paraconsistent semantics. In this paper, we consider the computational aspects of inconsistency degrees of propositional knowledge bases under 4-valued semantics. We first give a complete analysis of the computational complexity of computing inconsistency degrees. As it turns out that computing the exact inconsistency degree is intractable, we then propose an anytime algorithm that provides tractable approximations of the inconsistency degree from above and below. We show that our algorithm satisfies some desirable properties and give experimental results of our implementation of the algorithm.
%B International Journal of Software and Informatics
%P 3-21
%G eng
%0 Journal Article
%J Machine Learning
%D 2010
%T Concept Learning in Description Logics Using Refinement Operators
%A Jens Lehmann
%A Pascal Hitzler
%K description logics
%K Inductive logic programming
%K Refinement operators
%K Semantic Web
%K Structured machine learning
%X With the advent of the Semantic Web, description logics have become one of the most prominent paradigms for knowledge representation and reasoning. Progress in research and applications, however, is constrained by the lack of well-structured knowledge bases consisting of a sophisticated schema and instance data adhering to this schema. It is paramount that suitable automated methods for their acquisition, maintenance, and evolution will be developed. In this paper, we provide a learning algorithm based on refinement operators for the description logic ALCQ including support for concrete roles. We develop the algorithm from thorough theoretical foundations by identifying possible abstract property combinations which refinement operators for description logics can have. Using these investigations as a basis, we derive a practically useful complete and proper refinement operator. The operator is then cast into a learning algorithm and evaluated using our implementation DL-Learner. The results of the evaluation show that our approach is superior to other learning approaches on description logics, and is competitive with established ILP systems.
%B Machine Learning
%P 203-250
%G eng
%0 Conference Proceedings
%B ESWC 2011
%D 2010
%T Contextual Ontology Alignment of LOD with an Upper Ontology: A Case Study with Proton
%A Prateek Jain
%A Peter Yeh
%A Kunal Verma
%A Reymonrod Vasquez
%A Mariana Damova
%A Pascal Hitzler
%A Amit Sheth
%K ontology alignment and lod and proton
%B ESWC 2011
%I Springer
%C Heraklion, Greece
%V 6643
%P 80-92
%G eng
%R 10.1007/978-3-642-21034-1_6
%0 Conference Proceedings
%D 2010
%T Distance-based Measures of Inconsistency and Incoherency for Description Logics
%A Yue Ma
%A Pascal Hitzler
%X Inconsistency and incoherency are two sorts of erroneous information in a DL ontology which have been widely discussed in ontology-based applications. For example, they have been used to detect modeling errors during ontology construction. To provide more informative metrics which can tell the differences between inconsistent ontologies and between incoherent terminologies, there has been some work on measuring inconsistency of an ontology and on measuring incoherency of a terminology. However, most of them merely focus either on measuring inconsistency or on measuring incoherency and no clear ideas of how to extend them to allow for the other. In this paper, we propose a novel approach to measure DL ontologies, named distance-based measures. It has the merits that both inconsistency and incoherency can be measured in a unified framework. Moreover, only classical DL interpretations are used such that there is no restriction on the DL languages used.
%I 23rd International Workshop on Description Logics (DL2010)
%C Waterloo, Canada
%G eng
%0 Journal Article
%D 2010
%T Extracting Reduced Logic Programs from Artificial Neural Networks
%A Jens Lehmann
%A Sebastian Bader
%A Pascal Hitzler
%K artificial neural networks
%K reduced logic programs
%X Artificial neural networks can be trained to perform excellently in many application areas. While they can learn from raw data to solve sophisticated recognition and analysis problems, the acquired knowledge remains hidden within the network architecture and is not readily accessible for analysis or further use: Trained networks are *black boxes*. Recent research efforts therefore investigate the possibility to extract symbolic knowledge from trained networks, in order to analyze, validate, and reuse the structural insights gained implicitly during the training process. In this paper, we will study how knowledge in form of propositional logic programs can be obtained in such a way that the programs are as *simple* as possible - where *simple* is being understood in some clearly defined and meaningful way.
%G eng
%0 Conference Paper
%D 2010
%T Flexible Bootstrapping-Based Ontology Alignment
%A Prateek Jain
%A Pascal Hitzler
%A Amit Sheth
%K Ontology Matching and Wikipedia and BLOOMS and Plug-n-Play Ontology Matching System
%X BLOOMS (Jain et al, ISWC2010) is an ontology alignment system which, in its core, utilizes the Wikipedia category hierarchy for establishing alignments. In this paper, we present a Plug-and-Play extension to BLOOMS, which allows to flexibly replace or complement the use of Wikipedia by other online or offline resources, including domain-specific ontologies or taxonomies. By making use of automated translation services and of Wikipedia in languages other than English, it makes it possible to apply BLOOMS to alignment tasks where the input ontologies are written in different languages.
%I The Fifth International Workshop on Ontology Matching collocated with the 9th International Semantic Web Conference ISWC-2010, November 7, 2010
%G eng
%0 Book
%D 2010
%T Foundations of Semantic Web Technologies
%A Pascal Hitzler
%A Markus Krotzsch
%A Sebastian Rudolph
%K foundations of semantic web
%K foundations of semantic web technologies
%G eng
%0 Journal Article
%J The Computer Journal
%D 2010
%T Generalized Distance Functions in the Theory of Computation
%A Anthony K. Seda
%A Pascal Hitzler
%K denotational semantics
%K fixed-point theorems
%K logic programming
%K stable model
%K supported model
%K topology
%K ultra-metrics
%X We discuss a number of distance functions encountered in the theory of computation, including metrics, ultra-metrics, quasi-metrics, generalized ultrametrics, partial metrics, d-ultra-metrics, and generalized metrics. We consider their properties, associated fixed-point theorems, and some general applications they have within the theory of computation. We consider in detail the applications of generalized distance functions in giving a uniform treatment of several important semantics for logic programs, including acceptable programs and natural generalizations of them, and also the supported model and the stable model in the context of locally stratified extended disjunctive logic programs and databases.
%B The Computer Journal
%P 443-464
%G eng
%0 Conference Paper
%B Semantic Technology Conference 2010
%D 2010
%T How To Make Linked Data More than Data
%A Prateek Jain
%A Pascal Hitzler
%A Amit Sheth
%A Peter Z. Yeh
%A Kunal Verma
%K Linked Open Data
%K Lod federated query
%K LoD ontology
%K LoD Schema
%K LoD Schema Entichment
%K LoD Semantic Enrichment
%K SPARQL federated query
%X The LOD cloud has a potential for applicability in many AI-related tasks, such as open domain question answering, knowledge discovery, and the Semantic Web. An important prerequisite before the LOD cloud can enable these goals is allowing its users (and applications) to effectively pose queries to and retrieve answers from it. However, this prerequisite is still an open problem for the LOD cloud and has restricted it to 'merely more data.' To transform the LOD cloud from 'merely more data' to 'semantically linked data' there are plenty of open issues which should be addressed. We believe this transformation of the LOD cloud can be performed by addressing the shortcomings identified by us: lack of conceptual description of datasets, lack of expressivity, and difficulties with respect to querying.
%B Semantic Technology Conference 2010
%C San Francisco, California
%G eng
%0 Conference Paper
%B Dagstuhl Seminar Proceedings 10302
%D 2010
%T Learning Paradigms in Dynamic Environments
%A Barbara Hammer
%A Pascal Hitzler
%A Wolfgang Maass
%A Marc Toussaint
%X The seminar centered around problems which arise in the context of machine learning in dynamic environments. Particular emphasis was put on a couple of specific questions in this context: how to represent and abstract knowledge appropriately to shape the problem of learning in a partially unknown and complex environment and how to combine statistical inference and abstract symbolic representations; how to infer from few data and how to deal with non i.i.d. data, model revision and life-long learning; how to come up with efficient strategies to control realistic environments for which exploration is costly, the dimensionality is high and data are sparse; how to deal with very large settings; and how to apply these models in challenging application areas such as robotics, computer vision, or the web.
%B Dagstuhl Seminar Proceedings 10302
%I Schloss Dagstuhl
%C Dagstuhl, Germany
%G eng
%0 Conference Proceedings
%B 2010 AAAI Spring Symposium
%D 2010
%T Linked Data is Merely More Data
%A Prateek Jain
%A Pascal Hitzler
%A Peter Z. Yeh
%A Kunal Verma
%A Amit Sheth
%K Artificial Intelligence
%K Linked Data
%K Semantic Web
%K Web of Data
%X In this position paper, we argue that the Linked Open Data (LoD) Cloud, in its current form, is only of limited value for furthering the Semantic Web vision. Being merely a weakly linked 'triple collection', it will only be of very limited benefit for the AI or Semantic Web communities. We describe the corresponding problems with the LoD Cloud and give directions for research to remedy the situation.
%B 2010 AAAI Spring Symposium
%I AAAI Press
%C Menlo Park, California
%P 82-86
%@ 978-1-57735-461-1
%G eng
%0 Conference Paper
%B 23rd International Workshop on Description Logics (DL2010)
%D 2010
%T A MapReduce Algorithm for EL+
%A Raghava Mutharaju
%A Frederick Maier
%A Pascal Hitzler
%X Recently, the use of the MapReduce framework for distributed RDF Schema reasoning has shown that it is possible to compute the deductive closure of sets of over a billion RDF triples within a reasonable time span [22], and that it is also possible to carry the approach over to OWL Horst [21]. Following this lead, in this paper we provide a MapReduce algorithm for the description logic EL+, more precisely for the classification of EL+ ontologies. To do this, we first modify the algorithm usually used for EL+ classification. The modified algorithm can then be converted into a MapReduce algorithm along the same key ideas as used for RDF schema.
%B 23rd International Workshop on Description Logics (DL2010)
%C Waterloo, Canada
%G eng
%0 Book
%D 2010
%T Mathematical Aspects of Logic Programming Semantics
%A Anthony K. Seda
%A Pascal Hitzler
%G eng
%0 Generic
%D 2010
%T Nominal Schemas for Integrating Rules and Ontologies.
%A Frederick Maier
%A Adila Alfa Krisnadhi
%A Pascal Hitzler
%K Web Ontology Language and Description Logic and SROIQ and Semantic Web Rule Language and Datalog and tractability
%X We propose a description-logic style extension of OWL DL, which includes DL-safe variable SWRL and seamlessly integrates datalog rules. Our language also sports a tractable fragment, which we call ELP 2, covering OWL EL, OWL RL, most of OWL QL, and variable restricted datalog.
%G eng
%0 Conference Paper
%B 9th International Semantic Web Conference
%D 2010
%T Ontology Alignment for Linked Open Data
%A Prateek Jain
%A Pascal Hitzler
%A Amit Sheth
%A Kunal Verma
%A Peter Z. Yeh
%K BLOOMS
%K Linked Open Data
%K Linked Open Data Schema Matching
%K ontology alignment
%K Schema Alignment
%K Wikipedia
%X The Web of Data currently coming into existence through the Linked Open Data (LOD) effort is a major milestone in realizing the Semantic Web vision. However, the development of applications based on LOD faces difficulties due to the fact that the different LOD datasets are rather loosely connected pieces of information. In particular, links between LOD datasets are almost exclusively on the level of instances, and schema-level information is being ignored. In this paper, we therefore present a system for finding schema-level links between LOD datasets in the sense of ontology alignment. Our system, called BLOOMS, is based on the idea of bootstrapping information already present on the LOD cloud. We also present a comprehensive evaluation which shows that BLOOMS outperforms state-of-the-art ontology alignment systems on LOD datasets. At the same time, BLOOMS is also competitive compared with these other systems on the Ontology Evaluation Alignment Initiative Benchmark datasets.
%B 9th International Semantic Web Conference
%C Shanghai, China
%G eng
%0 Journal Article
%J Logic Journal of the IGPL
%D 2010
%T Perspectives and Challenges for Recurrent Neural Network Training
%A Marco Gori
%A Barbara Hammer
%A Pascal Hitzler
%A Guenther Palm
%K neural network training challenges
%X Recurrent neural networks (RNNs) offer flexible machine learning tools which share the learning abilities of feedforward networks and which extend their expression abilities based on dynamical equations. Hence, they can directly process complex spatiotemporal data and model complex dynamic systems. Since temporal and spatial data are present in many domains such as processing environmental time series, modelling the financial market, speech and language processing, robotics, bioinformatics, medical informatics, etc., RNNs constitute promising candidates for a variety of applications. Further, their rich dynamic repertoire as time dependent systems makes them suitable candidates for modelling brain phenomena or mimicking large-scale distributed computations and argumentations. Thus, RNNs carry the promise of efficient biologically plausible signal processing models optimally suited for a wide area of industrial applications on the one hand and an explanation of cognitive phenomena of the human brain on the other hand.
%B Logic Journal of the IGPL
%P 617-619
%G eng
%0 Conference Paper
%B SSDBM2010
%D 2010
%T Provenance Context Entity (PaCE): Scalable Provenance Tracking for Scientific RDF Data
%A Satya S. Sahoo
%A Krishnaprasad Thirunarayan
%A Olivier Bodenreider
%A Pascal Hitzler
%A Amit Sheth
%K Biomedical knowledge repository
%K Context theory
%K domain specific provenance
%K Model theoretic semantics
%K PACE
%K PrOM
%K Provenance context
%K Provenance context entity
%K Provenance Management Framework
%K Provenir ontology
%K RDF reification
%K semantic provenance
%X The Resource Description Framework (RDF) format is being used by a large number of scientific applications to store and disseminate their datasets. The provenance information, describing the source or lineage of the datasets, is playing an increasingly significant role in ensuring data quality, computing trust value of the datasets, and ranking query results. Current provenance tracking approaches using the RDF reification vocabulary suffer from a number of known issues, including lack of formal semantics, use of blank nodes, and application-dependent interpretation of reified RDF triples. In this paper, we introduce a new approach called Provenance Context Entity (PaCE) that uses the notion of provenance context to create provenance-aware RDF triples. We also define the formal semantics of PaCE through a simple extension of the existing RDF(S) semantics that ensures compatibility of PaCE with existing Semantic Web tools and implementations. We have implemented the PaCE approach in the Biomedical Knowledge Repository (BKR) project at the US National Library of Medicine. The evaluations demonstrate a minimum of 49% reduction in total number of provenance-specific RDF triples generated using the PaCE approach as compared to RDF reification. In addition, performance for complex queries improves by three orders of magnitude and remains comparable to the RDF reification approach for simpler provenance queries.
%B SSDBM2010
%I The 22nd International Conference on Scientific and Statistical Database Management (SSDBM) 2010
%G eng
%0 Conference Proceedings
%B Scientific and Statistical Database Management (SSDBM 2010)
%D 2010
%T Provenance Context Entity (PaCE): Scalable Provenance Tracking for Scientific RDF Data
%A Satya Sahoo
%A Olivier Bodenreider
%A Krishnaprasad Thirunarayan
%A Pascal Hitzler
%A Amit Sheth
%K Provenir ontology and Provenance context entity and Biomedical knowledge repository and Context theory and RDF reification
%X The Resource Description Framework (RDF) format is being used by a large number of scientific applications to store and disseminate their datasets. The provenance information, describing the source or lineage of the datasets, is playing an increasingly significant role in ensuring data quality, computing trust value of the datasets, and ranking query results. Current provenance tracking approaches using the RDF reification vocabulary suffer from a number of known issues, including lack of formal semantics, use of blank nodes, and application-dependent interpretation of reified RDF triples. In this paper, we introduce a new approach called Provenance Context Entity (PaCE) that uses the notion of provenance context to create provenance-aware RDF triples. We also define the formal semantics of PaCE through a simple extension of the existing RDF(S) semantics that ensures compatibility of PaCE with existing Semantic Web tools and implementations. We have implemented the PaCE approach in the Biomedical Knowledge Repository (BKR) project at the US National Library of Medicine. The evaluations demonstrate a minimum of 49% reduction in total number of provenance-specific RDF triples generated using the PaCE approach as compared to RDF reification. In addition, performance for complex queries improves by three orders of magnitude and remains comparable to the RDF reification approach for simpler provenance queries.
%B Scientific and Statistical Database Management (SSDBM 2010)
%C Heidelberg, Germany
%V 6187
%P 461-470
%G eng
%R 10.1007/978-3-642-13818-8_32
%0 Journal Article
%J Semantic Web – Interoperability, Usability, Applicability
%D 2010
%T A Reasonable Semantic Web
%A Frank Van Harmelen
%A Pascal Hitzler
%K Automated Reasoning
%K Formal Semantics
%K KnowledgeRepresentation
%K Linked Open Data
%X The realization of Semantic Web reasoning is central to substantiating the Semantic Web vision. However, current mainstream research on this topic faces serious challenges, which forces us to question established lines of research and to rethink the underlying approaches. We argue that reasoning for the Semantic Web should be understood as 'shared inference,' which is not necessarily based on deductive methods. Model-theoretic semantics (and sound and complete reasoning based on it) functions as a gold standard, but applications dealing with large-scale and noisy data usually cannot afford the required runtimes. Approximate methods, including deductive ones, but also approaches based on entirely different methods like machine learning or natureinspired computing need to be investigated, while quality assurance needs to be done in terms of precision and recall values (as in information retrieval) and not necessarily in terms of soundness and completeness of the underlying algorithms.
%B Semantic Web – Interoperability, Usability, Applicability
%I IOS Press
%P 39-44
%G eng
%0 Journal Article
%J Semantic Web
%D 2010
%T Semantic Web - Interoperability, Usability, Applicability
%A Pascal Hitzler
%A Krzysztof Janowicz
%K Applicability
%K Interoperability
%K Semantic Web
%K Usability
%X While this statement seems obvious, this has not been so a few years ago, when basic research funding seemed to be running out, and industrial uptake was hardly happening. In the meantime, we do not only see sustained funding for Semantic Web related research (in particular by the European Commission), but also significant investment by industry, including major IT and venture capital companies. The Semantic Web is here to stay – and to grow. The Semantic Web is multidisciplinary and heterogeneous. Many Semantic Web researchers maintain close ties to neighboring disciplines which provide methods or application areas for their work. However, the Semantic Web has now established itself as a research field in its own rights. Consequently, a growing number of researchers, in particular those of the second or third generation, seem to identify themselves with the Semantic Web as their primary field of work. The growing number of top quality events dedicated to Semantic Web topics is also a clear indication of this trend. Another indicator is the increasing interweavement of Semantic Web methods into related disciplines leading to research topics such as geospatialsemantics, the Semantic Sensor Web, semantic desktop, or work on cultural heritage
%B Semantic Web
%I IOS Press
%V 1
%P 1-2
%8 01/2010
%G eng
%R 10.3233/SW-2010-0017
%0 Conference Paper
%B Third International Conference, KSEM 2009
%D 2009
%T An Anytime Algorithm for Computing Inconsistency Measurement
%A Yue Ma
%A Guilin Qi
%A Guohui Xiao
%A Zuoquan Lin
%A Pascal Hitzler
%X Measuring inconsistency degrees of inconsistent knowledge bases is an important problem as it provides context information for facilitating inconsistency handling. Many methods have been proposed to solve this problem and a main class of them is based on some kind of paraconsistent semantics. In this paper, we consider the computational aspects of inconsistency degrees of propositional knowledge bases under 4-valued semantics. We first analyze its computational complexity. As it turns out that computing the exact inconsistency degree is intractable, we then propose an anytime algorithm that provides tractable approximation of the inconsistency degree from above and below.We show that our algorithm satisfies some desirable properties and give experimental results of our implementation of the algorithm.
%B Third International Conference, KSEM 2009
%G eng
%0 Conference Paper
%D 2009
%T An Evolutionary Computing Approach for Reasoning in the Semantic Web
%A Sebastian Rudolph
%A Gaston Tagni
%A Christophe Gueret
%A Stefan Schlobach
%A Pascal Hitzler
%I International Workshop on Collective Intelligence and Evolution
%G eng
%0 Journal Article
%J Kunstliche Intelligenz
%D 2009
%T Facets of Artificial General Intelligence
%A Kai-Uwe Kuhnberger
%A Pascal Hitzler
%X We argue that time has come for a serious endeavor to work towards artificial general intelligence (AGI). This positive assessment of the very possibility of AGI has partially its roots in the development of new methodological achievements in the AI area, like new learning paradigms and new integration techniques for different methodologies. The article sketches some of these methods as prototypical examples for approaches towards AGI.
%B Kunstliche Intelligenz
%P 58-59
%G eng
%0 Book
%D 2009
%T Foundations of Semantic Web Technologies
%A Sebastian Rudolph
%A Markus Krotzsch
%A Pascal Hitzler
%G eng
%0 Book Section
%D 2009
%T Ontologies and Rules
%A Bijan Parsia
%A Pascal Hitzler
%K OWL
%K Web Ontology Language
%X The Web Ontology Language OWL, as introduced in Chapter 4, is the language recommended by the World Wide Web consortium (W3C) for expressing ontologies for the Semantic Web. OWL is based on Description Logics, see Chapter 1, and as such is based on first-order predicate logic as underlying knowledge representation and reasoning paradigm.
%G eng
%0 Conference Paper
%B Third International Conference, RR
%D 2009
%T Paraconsistent Reasoning for OWL 2
%A Yue Ma
%A Pascal Hitzler
%X A four-valued description logic has been proposed to reason with description logic based inconsistent knowledge bases. This approach has a distinct advantage that it can be implemented by invoking classical reasoners to keep the same complexity as under the classical semantics. However, this approach has so far only been studied for the basid description logic ALC. In this paper, we further study how to extend the four-valued semantics to the more expressive description logic SROIQ which underlies the forthcoming revision of the Web Ontology Language, OWL 2, and also investigate how it fares when adapated to tractable description logics including EL++, DL-Lite, and Horn-DLs. We define the four-valued semantics along the same lines as for ALC and show that we can retain most of the desired properties.
%B Third International Conference, RR
%I Web Reasoning and Rule Systems, Third International Conference, RR 2009
%C Chantilly, VA, USA
%P 197-211
%8 10/2009
%G eng
%0 Conference Paper
%B International Conference, RR
%D 2009
%T A Preferential Tableaux Calculus for Circumscriptive ALCO
%A Stephan Grimm
%A Pascal Hitzler
%X Nonmonotonic extensions of description logics (DLs) allow for default and local closed-world reasoning and are an acknowledged desired feature for applications, e.g. in the Semantic Web. A recent approach to such an extension is based on McCarthy's circumscription, which rests on the principle of minimising the extension of selected predicates to close off dedicated parts of a domain model. While decidability and complexity results have been established in the literature, no practical algorithmisation for circumscriptive DLs has been proposed so far. In this paper, we present a tableaux calculus that can be used as a decision procedure for concept satisfiability with respect to concept circumscribed ALCO knowledge bases. The calculus builds on existing tableaux for classical DLs, extended by the notion of a preference clash to detect the non-minimality of constructed models.
%B International Conference, RR
%I International Conference, RR 2009
%C Chantilly, VA, USA
%P 40-54
%8 10/2009
%G eng
%0 Generic
%D 2009
%T PrOM: A Semantic Web Framework for Provenance Management in Science
%A Amit Sheth
%A Pascal Hitzler
%A Krishnaprasad Thirunarayan
%A Satya S. Sahoo
%A Roger Barga
%X The eScience paradigm is enabling researchers to collaborate over the Web in virtual laboratories and conduct experiments on an industrial scale. But, the inherent variability in the quality and trust associated with eScience resources necessitates the use of provenance information describing the origin of an entity. Existing systems often model provenance using ambiguous terminology, have poor domain semantics and include modeling inconsistencies that hinders interoperability. Further, mere collection of provenance information is of little value without a well-defined and scalable query mechanism. In this paper, we present 'PrOM', a framework that addresses both the modeling and querying issues in eScience provenance management. The theoretical underpinning for PrOM consists of, (a) a novel foundational ontology for provenance representation called 'Provenir', and (b) the first set of query operators to be defined for provenance query and analysis. The PrOM framework also includes a scalable provenance query engine that supports complex queries (high 'expression complexity') over a very large real world dataset with 308 million RDF triples. The query engine uses a new class of materialized views for query optimization that confers significant advantages (up to three orders of magnitude) in query performance.
%G eng
%0 Conference Paper
%D 2009
%T Suggestions for OWL 3
%A Pascal Hitzler
%X With OWL 2 about to be completed, it is the right time to start discussions on possible future modifications of OWL. We present here a number of suggestions in order to discuss them with the OWL user community. They encompass expressive extensions on polynomial OWL 2 profiles, a suggestion for an OWL Rules language, and expressive extensions for OWL DL.
%I 5th International Workshop on OWL: Experiences and Directions (OWLED 2009)
%G eng
%0 Conference Paper
%B Third International Conference, GeoS
%D 2009
%T Towards Reasoning Pragmatics
%A Pascal Hitzler
%X The realization of Semantic Web reasoning is central to substantiating the Semantic Web vision. However, current mainstream research on this topic faces serious challenges, which force us to question established lines of research and to rethink the underlying approaches.
%B Third International Conference, GeoS
%C Mexico City, Mexico
%8 12/2009
%G eng
%0 Conference Paper
%B Approximate OWL Instance Retrieval with Screech
%D 2008
%T Approximate OWL Instance Retrieval with Screech
%A Sebastian Rudolph
%A Markus Krotzsch
%A Tuvshintur Tserendorj
%A Pascal Hitzler
%X With the increasing interest in expressive ontologies for the Semantic Web, it is critical to develop scalable and efficient ontology reasoning techniques that can properly cope with very high data volumes. For certain application domains, approximate reasoning solutions, which trade soundness or completeness for increased reasoning speed, will help to deal with the high computational complexities which state of the art ontology reasoning tools have to face. In this paper, we present a comprehensive overview of the SCREECH approach to approximate instance retrieval with OWL ontologies, which is based on the KAON2 algorithms, facilitating a compilation of OWL DL TBoxes into Datalog, which is tractable in terms of data complexity. We present three different instantiations of the Screech approach, and report on experiments which show that the gain in efficiency outweighs the number of introduced mistakes in the reasoning process.
%B Approximate OWL Instance Retrieval with Screech
%G eng
%0 Conference Paper
%B International Conference, RR 2008
%D 2008
%T Approximate OWL-Reasoning with Screech
%A Sebastian Rudolph
%A Markus Krotzsch
%A Tuvshintur Tserendorj
%A Pascal Hitzler
%X Applications of expressive ontology reasoning for the Semantic Web require scalable algorithms for deducing implicit knowledge from explicitly given knowledge bases. Besides the development of more efficient such algorithms, awareness is rising that approximate reasoning solutions will be helpful and needed for certain application domains. In this paper, we present a comprehensive overview of the Screech approach to approximate reasoning with OWL ontologies, which is based on the KAON2 algorithms, facilitating a compilation of OWL DL TBoxes into Datalog, which is tractable in terms of data complexity.We present three different instantiations of the Screech approach, and report on experiments which show that a significant gain in efficiency can be achieved.
%B International Conference, RR 2008
%I Second International Conference, RR 2008
%C Karlsruhe, Germany
%P 165-180
%8 10/2008
%G eng
%0 Conference Paper
%B 11th European Conference on Logics in Artificial Intelligence (JELIA)
%D 2008
%T Cheap Boolean Role Constructors for Description Logics
%A Sebastian Rudolph
%A Markus Krotzsch
%A Pascal Hitzler
%X We investigate the possibility of incorporating Boolean role constructors on simple roles into some of today's most popular description logics, focussing on cases where those extensions do not increase complexity of reasoning. We show that the expressive DLs SHOIQ and SROIQ, serving as the logical underpinning of OWL and the forthcoming OWL 2, can accommodate arbitrary Boolean expressions. The prominent OWL-fragment SHIQ can be safely extended by safe role expressions, and the tractable fragments EL++ and DLP retain tractability if extended by conjunction on roles, where in the case of DLP the restriction on role simplicity can even be discarded.
%B 11th European Conference on Logics in Artificial Intelligence (JELIA)
%C Dresden, Germany
%P 362-374
%8 09/2008
%G eng
%0 Conference Paper
%B 18th European Conference on Artificial Intelligence, ECAI
%D 2008
%T A Coherent Well-founded Model for Hybrid MKNF Knowledge Bases
%A Matthias Knorr
%A Jose Julio Alferes
%A Pascal Hitzler
%X With the advent of the Semantic Web, the question becomes important how to best combine open-world based ontology languages, like OWL, with closed-world rules paradigms. One of the most mature proposals for this combination is known as Hybrid MKNF knowledge bases [11], which is based on an adaptation of the stable model semantics to knowledge bases consisting of ontology axioms and rules. In this paper, we propose a well-founded semantics for such knowledge bases which promises to provide better efficiency of reasoning, which is compatible both with the OWL-based semantics and the traditional well-founded semantics for logic programs, and which surpasses previous proposals for such a well-founded semantics by avoiding some issues related to inconsistency handling.
%B 18th European Conference on Artificial Intelligence, ECAI
%I 18th European Conference on Artificial Intelligence, ECAI 2008
%C Patras, Greece
%P 99-103
%8 07/2008
%G eng
%0 Journal Article
%J Neurocomputing
%D 2008
%T Connectionist Model Generation: A First-Order Approach
%A Sebastian Bader
%A Steffen Holldobler
%A Pascal Hitzler
%K Connectionist Model Generation
%K First-Order Logic Programs
%K Neural-Symbolic Integration
%K Recurrent RBF Networks
%X Knowledge based artificial neural networks have been applied quite successfully to propositional knowledge representation and reasoning tasks. However, as soon as these tasks are extended to structured objects and structure-sensitive processes as expressed e.g., by means of first-order predicate logic, it is not obvious at all what neural symbolic systems would look like such that they are truly connectionist, are able to learn, and allow for a declarative reading and logical reasoning at the same time. The core method aims at such an integration. It is a method for connectionist model generation using recurrent networks with feed-forward core.We show in this paper how the core method can be used to learn first-order logic programs in a connectionist fashion, such that the trained network is able to do reasoning over the acquired knowledge. We also report on experimental evaluations which show the feasibility of our approach.
%B Neurocomputing
%P 2420-2432
%G eng
%0 Conference Paper
%D 2008
%T Defeasible Inference with Circumscriptive OWL Ontologies
%A Stephan Grimm
%A Pascal Hitzler
%X The Web Ontology Language (OWL) adheres to the openworld assumption and can thus not be used for forms of nonmonotonic reasoning or defeasible inference, an acknowledged desirable feature in open Semantic Web environments. We investigate the use of the formalism of circumscriptive description logics (DLs) to realise defeasible inference within the OWL framework. By example, we demonstrate how reasoning with (restricted) circumscribed OWL ontologies facilitates various forms of defeasible inference, also in comparison to alternative approaches. Moreover, we sketch an extension to DL tableaux for handling the circumscriptive case and report on a preliminary implementation.
%I 5th European Semantic Web Conference, ESWC08
%G eng
%0 Conference Paper
%B The Semantic Web - ISWC 2008, 7th International Semantic Web Conference, 2008
%D 2008
%T Description Logic Reasoning with Decision Diagrams: Compiling SHIQ to Disjunctive Datalog
%A Sebastian Rudolph
%A Markus Krotzsch
%A Pascal Hitzler
%X We propose a novel method for reasoning in the description logic SHIQ. After a satisfiability preserving transformation from SHIQ to the description logic ALCIb, the obtained ALCIb Tbox T is converted into an ordered binary decision diagram (OBDD) which represents a canonical model for T. This OBDD is turned into a disjunctive datalog program that can be used for Abox reasoning. The algorithm is worst-case optimal w.r.t. data complexity, and admits easy extensions with DL-safe rules and ground conjunctive queries.
%B The Semantic Web - ISWC 2008, 7th International Semantic Web Conference, 2008
%I The Semantic Web - ISWC 2008, 7th International Semantic Web Conference
%C Karlsruhe, Germany
%P 435-450
%G eng
%0 Conference Paper
%B 18th European Conference on Artificial Intelligence, ECAI
%D 2008
%T Description Logic Rules
%A Sebastian Rudolph
%A Markus Krotzsch
%A Pascal Hitzler
%X We introduce description logic (DL) rules as a new rule-based formalism for knowledge representation in DLs. As a fragment of the Semantic Web Rule Language SWRL, DL rules allow for a tight integration with DL knowledge bases. In contrast to SWRL, however, the combination of DL rules with expressive description logics remains decidable, and we show that the DL SROIQ - the basis for the ongoing standardisation of OWL 2 - can completely internalise DL rules. On the other hand, DL rules capture many expressive features of SROIQ that are not available in simpler DLs yet. While reasoning in SROIQ is highly intractable, it turns out that DL rules can be introduced to various lightweight DLs without increasing their worst-case complexity. In particular, DL rules enable us to significantly extend the tractable DLs EL++ and DLP.
%B 18th European Conference on Artificial Intelligence, ECAI
%C Patras, Greece
%P 80-84
%8 07/2008
%G eng
%0 Report
%D 2008
%T ELP: Tractable Rules for OWL 2
%A Sebastian Rudolph
%A Markus Krotzsch
%A Pascal Hitzler
%X We introduce ELP as a decidable fragment of the Semantic Web Rule Language (SWRL) that admits reasoning in polynomial time. ELP is based on the tractable description logic EL++, and encompasses an extended notion of the recently proposed DL rules for that logic. Thus ELP extends EL++ with a number of features introduced by the forthcoming OWL 2, such as disjoint roles, local reflexivity, certain range restrictions, and the universal role. We present a reasoning algorithm based on a translation of ELP to Datalog, and this translation also enables the seamless integration of DL-safe rules into ELP. While reasoning with DL-safe rules as such is already highly intractable, we show that DL-safe rules based on the Description Logic Programming (DLP) fragment of OWL 2 can be admitted in ELP without losing tractability.
%B ELP: Tractable Rules for OWL 2
%G eng
%0 Conference Paper
%B ELP: Tractable Rules for OWL 2
%D 2008
%T ELP: Tractable Rules for OWL 2
%A Markus Krotzsch
%A Sebastian Rudolph
%A Pascal Hitzler
%X We introduce ELP as a decidable fragment of the Semantic Web Rule Language (SWRL) that admits reasoning in polynomial time. ELP is based on the tractable description logic EL++, and encompasses an extended notion of the recently proposed DL rules for that logic. Thus ELP extends EL++ with a number of features introduced by the forthcoming OWL 2, such as disjoint roles, local reflexivity, certain range restrictions, and the universal role.We present a reasoning algorithm based on a translation of ELP to Datalog, and this translation also enables the seamless integration of DL-safe rules into ELP.While reasoning with DL-safe rules as such is already highly intractable, we show that DL-safe rules based on the Description Logic Programming (DLP) fragment of OWL 2 can be admitted in ELP without losing tractability.
%B ELP: Tractable Rules for OWL 2
%G eng
%0 Generic
%D 2008
%T ELP: Tractable Rules for OWL 2
%A Markus Krotzsch
%A Sebastian Rudolph
%A Pascal Hitzler
%X We introduce ELP as a decidable fragment of the Semantic Web Rule Language (SWRL) that admits reasoning in polynomial time. ELP is based on the tractable description logic EL++, and encompasses an extended notion of the recently proposed DL rules for that logic. Thus ELP extends EL++ with a number of features introduced by the forthcoming OWL 2, such as disjoint roles, local reflexivity, certain range restrictions, and the universal role.We present a reasoning algorithm based on a translation of ELP to Datalog, and this translation also enables the seamless integration of DL-safe rules into ELP.While reasoning with DL-safe rules as such is already highly intractable, we show that DL-safe rules based on the Description Logic Programming (DLP) fragment of OWL 2 can be admitted in ELP without losing tractability.
%G eng
%0 Generic
%D 2008
%T Expressive Tractable Description Logics based on SROIQ Rules
%A Sebastian Rudolph
%A Markus Krotzsch
%A Pascal Hitzler
%X We introduce description logic (DL) rules as a new rule-based formalism for knowledge representation in DLs. As a fragment of the Semantic Web Rule Language SWRL, DL rules allow for a tight integration with DL knowledge bases. In contrast to SWRL, however, the combination of DL rules with expressive description logics remains decidable, and we show that the DL SROIQ - the basis for the ongoing standardisation of OWL 2 - can completely internalise DL rules. On the other hand, DL rules capture many expressive features of SROIQ that are not available in simpler DLs yet. While reasoning in SROIQ is highly intractable, it turns out that DL rules can be introduced to various lightweight DLs without increasing their worst-case complexity. In particular, DL rules enable us to significantly extend the tractable DLs EL++ and DLP.
%G eng
%0 Conference Paper
%D 2008
%T A Forgetting-based Approach for Handling Inconsistency in Distributed Ontologies
%A Guilin Qi
%A Yimin Wang
%A Peter Haase
%A Pascal Hitzler
%X In the context of multiple distributed ontologies, we are often confronted with the problem of dealing with inconsistency. In this paper, we propose an approach for reasoning with inconsistent distributed ontologies based on *concept forgetting*.We firstly define *concept forgetting* in description logics.We then adapt the notions of recoveries and preferred recoveries in propositional logic to description logics. Two consequence relations are then defined based on the preferred recoveries.
%I 5th European Semantic Web Conference, ESWC08
%G eng
%0 Book Section
%D 2008
%T Learning Expressive Ontologies
%A Johanna Volker
%A Peter Haase
%A Pascal Hitzler
%G eng
%0 Conference Paper
%D 2008
%T Paraconsistent Reasoning for Expressive and Tractable Description Logics
%A Yue Ma
%A Zuoquan Lin
%A Pascal Hitzler
%X Four-valued description logic has been proposed to reason with description logic based inconsistent knowledge bases, mainly ALC. This approach has a distinct advantage that it can be implemented by invoking classical reasoners to keep the same complexity as classical semantics. In this paper, we further study how to extend the four-valued semantics to more expressive description logics, such as SHIQ, and to more tractable description logics including EL++, DL-Lite, and Horn-DLs. The most effort we spend defining the four-valued semantics of expressive four-valued description logics is on keeping the reduction from four-valued semantics to classical semantics as in the case of ALC; While for tractable description logics, we mainly focus on how to maintain their tractability when adopting four-valued semantics.
%I 21st International Workshop on Description Logics, DL2008
%G eng
%0 Generic
%D 2008
%T Reasoning in Circumscriptive ALCO
%A Stephan Grimm
%A Pascal Hitzler
%X Non-monotonic extensions of description logics (DLs) allow for default and local closed-world reasoning and are an acknowledged desired feature for applications, e.g. in the Semantic Web. A recent approach to such an extension is based on McCarthy's circumscription, which rests on the principle of minimising the extension of selected predicates to locally close off dedicated parts of a domain model. While decidability and complexity results have been established in the literature, no practical algorithmisation for circumscriptive DLs has been proposed so far. In this paper, we present a tableaux calculus that can be used as a sound and complete decision procedure for concept satisfiability with respect to concept-circumscribed ALCO knowledge bases. The calculus builds on existing tableaux for classical DLs, extended by the notion of a preference clash to detect the non-minimality of constructed models.
%G eng
%0 Journal Article
%J International Journal of e-Commerce
%D 2008
%T Semantic Matchmaking of Web Resources with Local Closed-World Reasoning
%A Stephan Grimm
%A Pascal Hitzler
%K closed-world reasoning
%K local closed world reasoning
%X Ontology languages like OWL allow for semantically rich annotation of resources, such as products advertised at an electronic online marketplace,while the Description Logic (DL) formalism underlying OWL provides reasoning techniques to perform matchmaking on such annotations. We identify peculiarities in the use of DL inferences for matchmaking which are due to the open-world semantics of OWL, and we analyse the use of local closed-world reasoning for its applicability to matchmaking. In particular,we investigate two nonmonotonic extensions to DL, namely auto epistemic DLs and DLs with circumscription, for their suitability of realising local closed-world reasoning in the matchmaking context to overcome these problems. We discuss their different characteristics by means of an elab- orate example of an electronic marketplace for PC product catalogues from the eCommerce domain and demonstrate how these formalisms can be used to realise such scenarios.
%B International Journal of e-Commerce
%P 89-126
%G eng
%0 Book
%D 2008
%T Semantic Web. Grundlagen
%A Sebastian Rudolph
%A York Sure
%A Markus Krotzsch
%A Pascal Hitzler
%G eng
%0 Book Section
%B MINT (Mathematik, Informatik, Naturwissenschaften, Technik) Vol. 18
%D 2008
%T Spieltheorie
%A Pascal Hitzler
%A Pascal Hitzler
%A Alexander Chocholaty
%A Gudrun Kalmbach
%B MINT (Mathematik, Informatik, Naturwissenschaften, Technik) Vol. 18
%P 117-125
%G eng
%0 Conference Paper
%B Terminological Reasoning in SHIQ with Ordered Binary Decision Diagrams
%D 2008
%T Terminological Reasoning in SHIQ with Ordered Binary Decision Diagrams
%A Sebastian Rudolph
%A Markus Krotzsch
%A Pascal Hitzler
%X We present a new algorithm for reasoning in the description logic SHIQ, which is the most prominent fragment of the Web Ontology Language OWL. The algorithm is based on ordered binary decision diagrams (OBDDs) as a data structure for storing and operating on large model representations. We thus draw on the success and the proven scalability of OBDD-based systems. To the best of our knowledge, we present the very first algorithm for using OBDDs for reasoning with general Tboxes.
%B Terminological Reasoning in SHIQ with Ordered Binary Decision Diagrams
%G eng
%0 Generic
%D 2008
%T Terminological Reasoning in SHIQ with Ordered Binary Decision Diagrams
%A Sebastian Rudolph
%A Markus Krotzsch
%A Pascal Hitzler
%X We present a new algorithm for reasoning in the description logic SHIQ, which is the most prominent fragment of the Web Ontology Language OWL. The algorithm is based on ordered binary decision diagrams (OBDDs) as a data structure for storing and operating on large model representations. We thus draw on the success and the proven scalability of OBDD-based systems. To the best of our knowledge, we present the very first algorithm for using OBDDs for reasoning with general Tboxes.
%G eng
%0 Conference Paper
%B 4th European Semantic Web Conference
%D 2007
%T Acquisition of OWL DL Axioms from Lexical Resources
%A Johanna Volker
%A Philipp Cimiano
%A Pascal Hitzler
%X State-of-the-art research on automated learning of ontologies from text currently focuses on inexpressive ontologies. The acquisition of complex axioms involving logical connectives, role restrictions, and other expressive features of the Web Ontology Language OWL remains largely unexplored. In this paper, we present a method and implementation for enriching inexpressive OWL ontologies with expressive axioms which is based on a deep syntactic analysis of natural language definitions. We argue that it can serve as a core for a semi-automatic ontology engineering process supported by a methodology that integrates methods for both ontology learning and evaluation. The feasibility of our approach is demonstrated by generating complex class descriptions from Wikipedia definitions and from a fishery glossary provided by the Food and Agriculture Organization of the United Nations.
%B 4th European Semantic Web Conference
%C Innsbruck, Austria
%G eng
%0 Conference Paper
%B Proceedings of Ninth European Conference on Symbolic and Quanlitative Approaches to Reasoning with Uncertainty
%D 2007
%T An Algorithm for Computing Inconsistency Measurement by Paraconsistent Semantics
%A Yue Ma
%A Guilin Qi
%A Zuoquan Lin
%A Pascal Hitzler
%X Measuring inconsistency in knowledge bases has been recognized as an important problem in many research areas. Most of approaches proposed for measuring inconsistency are based on paraconsistent semantics. However, very few of them provide an algorithm for implementation. In this paper, we first give a four-valued semantics for first-order logic and then propose an approach for measuring the degree of inconsistency based on this four-valued semantics. After that, we propose an algorithm to compute the inconsistency degree by introducing a new semantics for first order logic, which is called S[n]-4 semantics.
%B Proceedings of Ninth European Conference on Symbolic and Quanlitative Approaches to Reasoning with Uncertainty
%C Hammamet,Tunisia
%P 91-102
%G eng
%0 Conference Paper
%B 4th European Semantic Web Conference, ESWC2007
%D 2007
%T Algorithms for Paraconsistent Reasoning with OWL
%A Yue Ma
%A Zuoquan Lin
%A Pascal Hitzler
%B 4th European Semantic Web Conference, ESWC2007
%C Innsbruck, Austria
%G eng
%0 Conference Paper
%B 30th Annual German Conference on AI
%D 2007
%T Any-World Access to OWL from Prolog
%A Tobias Matzner
%A Pascal Hitzler
%X The W3C standard OWL provides a decidable language for representing ontologies. While its use is rapidly spreading, efforts are being made by researchers worldwide to augment OWL with additional expressive features or by interlacing it with other forms of knowledge representation, in order to make it applicable for even further purposes. In this paper, we integrate OWL with one of the most successful and most widely used forms of knowledge representation, namely Prolog, and present a hybrid approach which layers Prolog on top of OWL in such a way that the open-world semantics of OWL becomes directly accessible within the Prolog system.
%B 30th Annual German Conference on AI
%I Advances in Artificial Intelligence, 30th Annual German Conference on AI, KI 2007
%C KI, Osnabruck, Germany
%P 84-98
%8 09/2007
%G eng
%0 Conference Paper
%D 2007
%T A Comparison of Disjunctive Well-founded Semantics
%A Matthias Knorr
%A Pascal Hitzler
%X While the stable model semantics, in the form of Answer Set Programming, has become a successful semantics for disjunctive logic programs, a corresponding satisfactory extension of the well-founded semantics to disjunctive programs remains to be found. The many current proposals for such an extension are so diverse, that even a systematic comparison between them is a challenging task. In order to aid the quest for suitable disjunctive well-founded semantics, we present a systematic approach to a comparison based on level mappings, a recently introduced framework for characterizing logic programming semantics, which was quite successfully used for comparing the major semantics for normal logic programs. We extend this framework to disjunctive logic programs, which will allow us to gain comparative insights into their different handling of negation. Additionally, we show some of the problems occurring when trying to handle minimal models (and thus disjunctive stable models) within the framework.
%I Foundations of Artificial Intelligence (FAInt-07)
%G eng
%0 Conference Paper
%B The 22nd AAAI Conference on Artficial Intelligence
%D 2007
%T Complexity Boundaries for Horn Description Logics
%A Sebastian Rudolph
%A Markus Krotzsch
%A Pascal Hitzler
%X Horn description logics (Horn-DLs) have recently started to attract attention due to the fact that their (worst-case) data complexities are in general lower than their overall (i.e. combined) complexities, which makes them attractive for reasoning with large ABoxes. However, the natural question whether Horn-DLs also provide advantages for TBox reasoning has hardly been addressed so far. In this paper, we therefore provide a thorough and comprehensive analysis of the combined complexities of Horn-DLs. While the combined complexity for many Horn-DLs turns out to be the same as for their non-Horn counterparts, we identify subboolean DLs where Hornness simplifies reasoning.
%B The 22nd AAAI Conference on Artficial Intelligence
%C Vancouver, British Columbia, Canada
%G eng
%0 Generic
%D 2007
%T Complexity of Horn Description Logics
%A Sebastian Rudolph
%A Markus Krotzsch
%A Pascal Hitzler
%X Horn description logics (Horn-DLs) have recently started to attract attention due to the fact that their (worst-case) data complexities are in general lower than their overall (i.e. combined) complexities, which makes them attractive for reasoning with large ABoxes. However, the natural question whether Horn-DLs also provide advantages for TBox reasoning has hardly been addressed so far. In this paper, we therefore provide a thorough and comprehensive analysis of the combined complexities of Horn-DLs. While the combined complexity for many Horn-DLs turns out to be the same as for their non-Horn counterparts, we identify subboolean DLs where Hornness simplifies reasoning.
%G eng
%0 Conference Paper
%B 6th International Semantic Web Conference, 2nd Asian Semantic Web Conference, ISWC 2007 + ASWC
%D 2007
%T Conjunctive Queries for a Tractable Fragment of OWL 1.1
%A Sebastian Rudolph
%A Markus Krotzsch
%A Pascal Hitzler
%X Despite the success of the Web Ontology Language OWL, the development of expressive means for querying OWL knowledge bases is still an open issue. In this paper, we investigate how a very natural and desirable form of queries-namely conjunctive ones-can be used in conjunction with OWL such that one of the major design criteria of the latter-namely decidability-can be retained. More precisely, we show that querying the tractable fragment EL++ of OWL 1.1 is decidable. We also provide a complexity analysis and show that querying unrestricted EL++ is undecidable.
%B 6th International Semantic Web Conference, 2nd Asian Semantic Web Conference, ISWC 2007 + ASWC
%I The Semantic Web, 6th International Semantic Web Conference, 2nd Asian Semantic Web Conference, ISWC 2007 + ASWC
%C Busan, Korea
%P 310-323
%8 11/2007
%G eng
%0 Book Section
%D 2007
%T The Core Method: Connectionist Model Generation for First-Order Logic Programs
%A Sebastian Bader
%A Steffen Holldobler
%A Andreas Witzel
%A Pascal Hitzler
%K Artificial Intelligence
%X In Artificial Intelligence, knowledge representation studies the formalisation of knowledge and its processing within machines. Techniques of automated reasoning allow a computer system to draw conclusions from knowledge represented in a machine-interpretable form. Recently, ontologies have evolved in computer science as computational artefacts to provide computer systems with a conceptual yet computational model of a particular domain of interest. In this way, computer systems can base decisions on reasoning about domain knowledge, similar to humans. This chapter gives an overview on basic knowledge representation aspects and on ontologies as used within computer systems. After introducing ontologies in terms of their appearance, usage and classification, it addresses concrete ontology languages that are particularly important in the context of the Semantic Web. The most recent and predominant ontology languages and formalisms are presented in relation to each other and a selection of them is discussed in more detail.
%G eng
%0 Conference Paper
%B First International Conference on Web Reasoning and Rule Systems, RR2007
%D 2007
%T Decidability Under the Well-Founded Semantics
%A Pascal Hitzler
%A Natalia Cherchago
%A Steffen Holldobler
%X The well-founded semantics (WFS) for logic programs is one of the few major paradigms for closed-world reasoning. With the advent of the Semantic Web, it is being used as part of rule systems for ontology reasoning, and also investigated as to its usefulness as a semantics for hybrid systems featuring combined open- and closed-world reasoning. Even in its most basic form, however, the WFS is undecidable. In fact, it is not even semi-decidable, which means that it is a theoretical impossibility that sound and complete reasoners for the WFS exist. Surprisingly, however, this matter has received next to no attention in research, although it has already been shown in 1995 by John Schlipf [1]. In this paper, we present several conditions under which query-answering under the well-founded semantics is decidable or semi-decidable. To the best of our knowledge, these are the very first results on such conditions.
%B First International Conference on Web Reasoning and Rule Systems, RR2007
%C Innsbruck, Austria
%G eng
%0 Conference Paper
%D 2007
%T Description Logic Programs: Normal Forms
%A Andreas Eberhart
%A Pascal Hitzler
%X The relationship and possible interplay between different knowledge representation and reasoning paradigms is a fundamental topic in artificial intelligence. For expressive knowledge representation for the Semantic Web, two different paradigms - namely Description Logics (DLs) and Logic Programming - are the two most successful approaches. A study of their exact relationships is thus paramount. An intersection of OWL with (function-free non-disjunctive) Datalog, called DLP (for Description Logic Programs), has been described in [1,2]. We provide normal forms for DLP in Description Logic syntax and in Datalog syntax, thus providing a bridge for the researcher and user who is familiar with either of these paradigms. We argue that our normal forms are the most convenient way to define DLP for teaching and dissemination purposes.
%I FAInt-07
%G eng
%0 Conference Paper
%B International Conference on Web Reasoning and Rule Systems, RR2007
%D 2007
%T Efficient OWL Reasoning with Logic Programs - Evaluations
%A Sebastian Rudolph
%A Markus Krotzsch
%A Michael Sintek
%A Denny Vrandecic
%A Pascal Hitzler
%X We report on efficiency evaluations concerning two different approaches to using logic programming for OWL [1] reasoning and show, how the two approaches can be combined. Introduction. Scalability of reasoning remains one of the major obstacles in leveraging the full power of the Web Ontology Language OWL [1] for practical applications. Among the many possible approaches to address scalability, one of them concerns the use of logic programming for this purpose. It was recently shown that reasoning in Horn-SHIQ [2-4] can be realised by invoking Prolog systems on the output of the
%B International Conference on Web Reasoning and Rule Systems, RR2007
%C Innsbruck, Austria
%P 370-373
%G eng
%0 Conference Paper
%B 17th International Conference, ILP 2007
%D 2007
%T Foundations of Refinement Operators for Description Logics
%A Jens Lehmann
%A Pascal Hitzler
%X In order to leverage techniques from Inductive Logic Programming for the learning in description logics (DLs), which are the foundation of ontology languages in the Semantic Web, it is important to acquire a thorough understanding of the theoretical potential and limitations of using refinement operators within the description logic paradigm. In this paper, we present a comprehensive study which analyses desirable properties such operators should have. In particular, we show that ideal refinement operators in general do not exist, which is indicative of the hardness inherent in learning in DLs. We also show which combinations of desirable properties are theoretically possible, thus providing an important step towards the definition of practically applicable operators.
%B 17th International Conference, ILP 2007
%C Corvallis, OR, USA
%P 161-174
%8 06/2007
%G eng
%0 Conference Paper
%B Twentieth International Joint Conference on Artificial Intelligence, IJCAI-07
%D 2007
%T A Fully Connectionist Model Generator for Covered First-Order Logic Programs
%A Sebastian Bader
%A Steffen Holldobler
%A Andreas Witzel
%A Pascal Hitzler
%X We present a fully connectionist system for the learning of first-order logic programs and the generation of corresponding models: Given a program and a set of training examples, we embed the associated semantic operator into a feed-forward network and train the network using the examples. This results in the learning of first-order knowledge while damaged or noisy data is handled gracefully.
%B Twentieth International Joint Conference on Artificial Intelligence, IJCAI-07
%C Hyderabad, India
%P 666-671
%G eng
%0 Book Section
%D 2007
%T Kursarbeit mit Schulern - die Intensivkurse Mathematik
%A Gudrun Kalmbach
%A Pascal Hitzler
%G eng
%0 Conference Paper
%D 2007
%T Measuring Inconsistency for Description Logics Based on Paraconsistent Semantics
%A Yue Ma
%A Guilin Qi
%A Pascal Hitzler
%A Zuoquan Lin
%X In this paper, we present an approach for measuring inconsistency in a knowledge base.We first define the degree of inconsistency using a four-valued semantics for the description logic ALC. Then an ordering over knowledge bases is given by considering their inconsistency degrees. Our measure of inconsistency can provide important information for inconsistency handling.
%I the 2007 International Workshop on Description Logics (DL-2007)
%G eng
%0 Conference Paper
%B Ninth European Conference on Symbolic and Quanlitative Approaches to Reasoning with Uncertainty
%D 2007
%T Measuring Inconsistency for Description Logics Based on Paraconsistent Semantics
%A Yue Ma
%A Guilin Qi
%A Zuoquan Lin
%A Pascal Hitzler
%X In this paper, we present an approach for measuring inconsistency in a knowledge base.We first define the degree of inconsistency using a four-valued semantics for the description logic ALC. Then an ordering over knowledge bases is given by considering their inconsistency degrees. Our measure of inconsistency can provide important information for inconsistency handling.
%B Ninth European Conference on Symbolic and Quanlitative Approaches to Reasoning with Uncertainty
%C Hammamet, Tunisia
%G eng
%0 Conference Paper
%D 2007
%T Paraconsistent Resolution for Four-valued Description Logics
%A Yue Ma
%A Zuoquan Lin
%A Pascal Hitzler
%X In this paper, we propose an approach to translating any *ALC* ontology (possible inconsistent) into a logically consistent set of disjunctive datalog rules. We achieve this in two steps: First we give a simple way to make any *ALC* based ontology 4-valued satisfiable, and then we study a sound and complete paraconsistent ordered-resolution decision procedure for our 4-valued *ALC*. Our approach can be viewed as a paraconsistent version of KAON2 algorithm.
%I the 2007 International Workshop on Description Logics (DL-2007)
%G eng
%0 Conference Paper
%B ICCS 2007
%D 2007
%T Quo Vadis, CS? - On the (non)-impact of Conceptual Structures on the Semantic Web
%A Sebastian Rudolph
%A Markus Krotzsch
%A Pascal Hitzler
%X Conceptual Structures is a field of research which shares abstract concepts and interests with recent work on knowledge representation for the Semantic Web. However, while the latter is an area of research and development which is rapidly expanding in recent years, the former fails to participate in these developments on a large scale. In this paper, we attempt to stimulate the Conceptual Structures community to catch the Semantic Web train.
%B ICCS 2007
%C Sheffield, UK
%G eng
%0 Conference Paper
%B 17th International Conference, ILP
%D 2007
%T A Refinement Operator Based Learning Algorithm for the ALC Description Logic
%A Jens Lehmann
%A Pascal Hitzler
%X With the advent of the Semantic Web, description logics have become one of the most prominent paradigms for knowledge representation and reasoning. Progress in research and applications, however, faces a bottleneck due to the lack of available knowledge bases, and it is paramount that suitable automated methods for their acquisition will be developed. In this paper, we provide the first learning algorithm based on refinement operators for the most fundamental description logic ALC. We develop the algorithm from thorough theoretical foundations and report on a prototype implementation.
%B 17th International Conference, ILP
%I 17th International Conference, ILP 2007
%C Corvallis, OR, USA
%P 147-160
%8 06/2007
%G eng
%0 Conference Paper
%B 13th Portuguese Conference on Aritficial Intelligence, EPIA
%D 2007
%T Towards Tractable Local Closed World Reasoning for the Semantic Web
%A Matthias Knorr
%A Jose Julio Alferes
%A Pascal Hitzler
%X Recently, the logics of minimal knowledge and negation as failure MKNF [12] was used to introduce hybrid MKNF knowledge bases [14], a powerful formalism for combining open and closed world reasoning for the Semantic Web. We present an extension based on a new three-valued framework including an alternating fixpoint, the well-founded MKNF model. This approach, the well-founded MKNF semantics, derives its name from the very close relation to the corresponding semantics known from logic programming. We show that the well-founded MKNF model is the least model among all (three-valued) MKNF models, thus soundly approximating also the two-valued MKNF models from [14]. Furthermore, its computation yields better complexity results (up to polynomial) than the original semantics where models usually have to be guessed.
%B 13th Portuguese Conference on Aritficial Intelligence, EPIA
%I 13th Portuguese Conference on Aritficial Intelligence, EPIA 2007
%C Guimaraes, Portugal
%P 3-14
%8 12/2007
%G eng
%0 Conference Paper
%D 2007
%T A Well-founded Semantics for Hybrid MKNF Knowledge Bases
%A Matthias Knorr
%A Jose Julio Alferes
%A Pascal Hitzler
%X In [10], hybrid MKNF knowledge bases have been proposed for combining open and closed world reasoning within the logics of minimal knowledge and negation as failure ([8]). For this powerful framework, we define a three-valued semantics and provide an alternating fixpoint construction for nondisjunctive hybrid MKNF knowledge bases. We thus provide a well-founded semantics which is a sound approximation of the cautious MKNF model semantics, and which also features improved computational properties. We also show that whenever the DL knowledge base part is empty, then the alternating fixpoint coincides with the classical well-founded model.
%I the 2007 International Workshop on Description Logics (DL-2007)
%G eng
%0 Conference Paper
%D 2006
%T On the Complexity of Horn Description Logics
%A Sebastian Rudolph
%A Markus Krotzsch
%A Pascal Hitzler
%X Horn-*SHIQ* has been identified as a fragment of the description logic *SHIQ* for which inferencing is in PT_{IME} with respect to the size of the ABox. This enables reasoning with larger ABoxes in situations where the TBox is static, and represents one approach towards tractable description logic reasoning. In this paper, we show that reasoning in Horn-*SHIQ*, in spite of its low datacomplexity, is E_{xp}T_{IME}-hard with respect to the overall size of the knowledge base. While this result is not unexpected, the proof is not a mere modification of existing reductions since it has to account for the restrictions of Hornness. We establish the result for Horn-*FLE*, showing that Hornness does not simplify TBox reasoning even for very restricted description logics. Moreover, we derive a context-free grammar that defines Horn-*SHIQ* in a simpler and more intuitive way than existing characterisations.
%I Second Workshop OWL - Experiences and Directions, OWLED2006
%G eng
%0 Conference Paper
%B the Second International Conference on Rules and Rule Markup Languages for the Semantic Web, RuleML2006
%D 2006
%T How to Reason with OWL in a Logic Programming System
%A M. Krotzsch
%A D. Vrandecic
%A M. Sintek
%A Pascal Hitzler
%X Logic programming has always been a major ontology modeling paradigm, and is frequently being used in large research projects and industrial applications, e.g., by means of the F-Logic reasoning engine OntoBroker or the TRIPLE query, inference, and transformation language and system. At the same time, the Web Ontology Language OWL has been recommended by the W3C for modeling ontologies for the web. Naturally, it is desirable to investigate the interoperability between both paradigms. In this paper, we do so by studying an expressive fragement of OWL DL for which reasoning can be reduced to the evaluation of Horn logic programs. Building on the KAON2 algorithms for transforming OWL DL into disjunctive Datalog, we give a detailed account of how and to what extent OWL DL can be employed in standard logic programming systems. En route, we derive a novel, simplified characterization of the supported fragment of OWL DL.
%B the Second International Conference on Rules and Rule Markup Languages for the Semantic Web, RuleML2006
%C Athens, Georgia
%P 17-26
%G eng
%0 Conference Paper
%B 3rd European Semantic Web Conference (ESWC 2006)
%D 2006
%T Integrating Semantic Web Services for Mobile Access
%A Anupriya Ankolekar
%A Pascal Hitzler
%A Holger Lewen
%A Daniel Oberle
%A Rudi Studer
%X We present our work in integrating Semantic Web services for access via mobile devices. We have developed a system, the WebServiceAccessComponent, that transforms a user request for a service on a mobile device, to a Web service request and then selects a matching service from the existing Web services of the Deutsche Telekom, which provide navigational and weather information. In this poster, we present the requirements and design of the WebServiceAccessComponent.
%B 3rd European Semantic Web Conference (ESWC 2006)
%C Budva, Montenegro
%G eng
%0 Conference Paper
%B 3rd European Semantic Web Conference, ESWC 2006
%D 2006
%T A Metamodel and UML Profile for Rule-extended OWL DL Ontologies
%A R. Studer
%A S. Brockmans
%A P. Haase
%A Pascal Hitzler
%X In this paper we present a MOF compliant metamodel and UML profile for the Semantic Web Rule Language (SWRL) that integrates with our previous work on a metamodel and UML profile for OWL DL. Based on this metamodel and profile, UML tools can be used for visual modeling of rule-extended ontologies.
%B 3rd European Semantic Web Conference, ESWC 2006
%C Budva, Montenegro
%P 303-316
%G eng
%0 Conference Paper
%B 14th International Conference on Conceptual Structures, ICCS 2006
%D 2006
%T Querying Formal Contexts with Answer Set Programs
%A M. Krotzsch
%A Pascal Hitzler
%X Recent studies showed how a seamless integration of formal concept analysis (FCA), logic of domains, and answer set programming (ASP) can be achieved. Based on these results for combining hierarchical knowledge with classical rule-based formalisms, we introduce an expressive common-sense query language for formal contexts. Although this approach is conceptually based on order-theoretic paradigms, we show how it can be implemented on top of standard ASP systems. Advanced features, such as default negation and disjunctive rules, thus become practically available for processing contextual data.
%B 14th International Conference on Conceptual Structures, ICCS 2006
%C Aalborg, Denmark
%P 260-273
%G eng
%0 Journal Article
%J IEEE Intelligent Systems
%D 2006
%T A Semantic Future for AI
%A R. Studer
%A A. Ankolekar
%A Pascal Hitzler
%K AI
%K Semantics of AI
%X In our modern information society, people need to manage ever-increasing numbers of personal devices and conduct more of their work and activities online, often making use of heterogeneous services. The amount of information to be processed by each individual is constantly growing, making it increasingly difficult to control, channel, share and make constructive use of it. To mitigate this, computing needs to become much more human-centered, e.g. by presenting personalised information to users and by respecting personal preferences in controlling multiple devices or invoking various services. Appropriate representation of the semantics of the information and functionality of devices and services will be critical to such personalised computing. Symbolic artificial intelligence (AI) techniques provide the method of choice for the required semantic representation and reasoning capabilities. The challenge for symbolic AI is to be able to support large-scale, distributed, dynamic knowledge bases enabling highly adaptive and evolving systems. AI must also look to specific application contexts and develop real-world solutions for problems in those domains. Below, we present some examples of such application contexts.
%B IEEE Intelligent Systems
%P 8-9
%G eng
%0 Book Section
%D 2006
%T Visual Ontology Modeling for Electronic Markets
%A Rudi Studer
%A Saartje Brockmans
%A Andreas Geyer-Schulz
%A Pascal Hitzler
%X The research program, Information Management and Market Engineering, focuses on the analysis and the design of electronic markets. Taking a holistic view of the conceptualization and realization of solutions, the research integrates the disciplines business administration, economics, computer science, and law. Topics of interest range from the implementation, quality assurance, and further development of electronic markets to their integration into business processes, innovative business models, and legal frameworks.
%G eng
%0 Book Section
%D 2005
%T Automatisiertes Schließen mit formalen Begriffen: Mathematische Grundlagen
%A Pascal Hitzler
%G eng
%0 Book Section
%D 2005
%T Automatisiertes Schließen mit formalen Begriffen: Mathematische Grundlagen
%A Pascal Hitzler
%G eng
%0 Conference Paper
%D 2005
%T Bridging the Paradigm Gap with Rules for OWL
%A Rudi Studer
%A Jurgen Angele
%A Boris Motik
%A Pascal Hitzler
%X Accelerated by the vision of the semantic web, semantic technologies have recently made significant advances. The underlying methods and paradigms are already being transferred to adjacent areas of research in artificial intelligence, knowledge management, and elsewhere. Textbooks explaining the foundations have appeared. Large national and international projects on the topic are under way.
%I W3C Workshop on Rule Languages for Interoperability
%G eng
%0 Conference Paper
%B Eighteenth International Florida Artificial Intelligence Research Symposium Conference
%D 2005
%T Computing First-Order Logic Programs by Fibring Artificial Neural Networks
%A Sebastian Bader
%A Artur S. D'A. Garcez
%A Pascal Hitzler
%X The integration of symbolic and neural-network-based artificial intelligence paradigms constitutes a very challenging area of research. The overall aim is to merge these two very different major approaches to intelligent systems engineering while retaining their respective strengths. For symbolic paradigms that use the syntax of some first-order language this appears to be particularly difficult. In this paper, we will extend on an idea proposed by Garcez and Gabbay (2004) and show how first-order logic programs can be represented by fibred neural networks. The idea is to use a neural network to iterate a global counter n. For each clause C_{i} in the logic program, this counter is combined (fibred) with another neural network, which determines whether C_{i} outputs an atom of level *n* for a given interpretation *I*. As a result, the fibred network computes the singlestep operator T_{P} of the logic program, thus capturing the semantics of the program.
%B Eighteenth International Florida Artificial Intelligence Research Symposium Conference
%C Clearwater Beach, Florida, USA
%G eng
%0 Conference Paper
%D 2005
%T Description Logic Programs: A Practical Choice For the Modelling of Ontologies
%A York Sure
%A Rudi Studer
%A Pascal Hitzler
%X Knowledge representation using ontologies constitutes the heart of semantic technologies. Despite successful standardization e.orts by the W3C, however, there are still numerous di.erent ontology representation languages being used, and interoperability between them is in general not given. The problem is aggrevated by the fact that current standards lay foundations only and are well-known to be insufficient for the modelling of finer details. Thus, a plethora of extensions of the basic languages is being proposed, rendering the picture of ontology representation languages to be chaotic, to say the least. While semantic technologies start to become applicable and are being applied in adjacent areas of research and in research projects with industrial participation, and can soon be expected to become an integral part of industrial applications, the practitioner is faced with the difficult task of choosing his basic ontology representation paradigm. We will argue that the OWL subset known as Description Logic Programs constitutes a very reasonable choice.
%I 1st Workshop on Formal Ontologies meet Meet Industry, FOMI'05
%G eng
%0 Book Section
%D 2005
%T Dimensions of Neural-Symbolic Integration - A Structured Survey
%A Sebastian Bader
%A Pascal Hitzler
%G eng
%0 Conference Paper
%D 2005
%T DLP Isn't So Bad After All
%A York Sure
%A Rudi Studer
%A Markus Krotzsch
%A Peter Haase
%A Pascal Hitzler
%X We discuss some of the recent controversies concerning the DLP fragment of OWL. We argue that it is a meaningful fragment and can serve as a basic interoperability layer between OWL and logic programming-based ontology languages.
%G eng
%0 Conference Paper
%B DLP Isn't So Bad After All
%D 2005
%T DLP Isn't So Bad After All
%A Pascal Hitzler
%A York Sure
%A Rudi Studer
%A Markus Krotzsch
%A Peter Haase
%B DLP Isn't So Bad After All
%G eng
%0 Conference Paper
%D 2005
%T Faster OWL Using Split Programs
%A Denny Vrandecic
%A Pascal Hitzler
%X Knowledge representation and reasoning on the Semantic Web is done by means of ontologies. While the quest for suitable ontology languages is still ongoing, OWL [5] has been established as a core standard. It comes in three flavours, as OWL Full, OWL DL and OWL Lite, where OWL Full contains OWL DL, which in turn contains OWL Lite. The latter two coincide semantically with certain description logics and can thus be considered fragments of first-order predicate logic.
%G eng
%0 Conference Paper
%D 2005
%T Level Mapping Characterizations of Selector-Generated Models for Logic Programs
%A Sibylle Schwarz
%A Pascal Hitzler
%K Selector-Generated Models
%X Assigning semantics to logic programs via selector generated models (Schwarz 2002/2003) extends several semantics, like the stable, the inflationary, and the stable generated semantics, to programs with arbitrary formulae in rule heads and bodies. We study this approach by means of a unifying framework for characterizing different logic programming semantics using level mappings (Hitzler and Wendt 200x, Hitzler 2003), thereby supporting the claim that this framework is very flexible and applicable to very diversely defined semantics.
%I 19th Workshop on (Constraint) Logic Programming
%G eng
%0 Conference Paper
%D 2005
%T Modeling Fuzzy Rules with Description Logics
%A Sudhir Agarwal
%A Pascal Hitzler
%X In real application scenarios, input data and knowledge is often vague. Likewise, it is often the case that exact reasoning over data is impossible due to complex dependencies between input data and target outputs. For practical applications, however, good approximations often suffice, and efficient calculation of an approximate answer is often preferable over complex processing which may take a long time to come up with an exact answer. Fuzzy logic supports both features by providing fuzzy membership functions and fuzzy IF-THEN rule bases. In this paper, we show how fuzzy membership functions and fuzzy rules can be modeled by means of an appropriate description logic and how this can be employed for query answering.
%G eng
%0 Conference Paper
%B 13th International Conference on Conceptual Structures, ICCS '05
%D 2005
%T Morphisms in Context
%A Markus Krotzsch
%A Guo-Qiang Zhang
%A Pascal Hitzler
%X Morphisms constitute a general tool for modelling complex relationships between mathematical objects in a disciplined fashion. In Formal Concept Analysis (FCA), morphisms can be used for the study of structural properties of knowledge represented in formal contexts, with applications to data transformation and merging. In this paper we present a comprehensive treatment of some of the most important morphisms in FCA and their relationships, including dual bonds, scale measures, infomorphisms, and their respective relations to Galois connections. We summarize our results in a concept lattice that cumulates the relationships among the considered morphisms. The purpose of this work is to lay a foundation for applications of FCA in ontology research and similar areas, where morphisms help formalize the interplay among distributed knowledge bases.
%B 13th International Conference on Conceptual Structures, ICCS '05
%C Kassel, Germany
%P 223-237
%G eng
%0 Conference Paper
%B Ontology Learning as a Use Case for Neural-Symbolic Integration
%D 2005
%T Ontology Learning as a Use Case for Neural-Symbolic Integration
%A Sebastian Bader
%A Artur S. D'Avila Garcez
%A Pascal Hitzler
%X We argue that the field of neural-symbolic integration is in need of identifying application scenarios for guiding further research. We furthermore argue that ontology learning - as occuring in the context of semantic technologies - provides such an application scenario with potential for success and high impact on neural-symbolic integration.
%B Ontology Learning as a Use Case for Neural-Symbolic Integration
%G eng
%0 Conference Paper
%B ISWC2005
%D 2005
%T Resolution-based approximate reasoning for OWL DL
%A Denny Vrandecic
%A Pascal Hitzler
%X We propose a new technique for approximate ABox reasoning with OWL DL ontologies. Essentially, we obtain substantially improved reasoning performance by disregarding non-Horn features of OWL DL. Our approach comes as a side-product of recent research results concerning a new transformation of OWL DL ontologies into negation-free disjunctive datalog [1, 2, 3, 4], and rests on the idea of performing standard resolution over disjunctive rules by treating them as if they were non-disjunctive ones. We analyse our reasoning approach by means of non-monotonic reasoning techniques, and present an implementation, called Screech.
%B ISWC2005
%C Galway, Ireland
%P 383-397
%G eng
%0 Conference Paper
%D 2005
%T Semantic Management of Web Services using the Core Ontology of Services
%A Stephan Grimm
%A Andreas Eberhart
%A Rudi Studer
%A Sudhir Agarwal
%A Daniel Oberle
%A Steffen Lamparter
%A Pascal Hitzler
%X Different Web Service standards like WSDL, WS-Security, WS-Policy etc., henceforth referred to as WS*, factorize Web Service management tasks into different aspects, such as input/output, workflow, or security. The advantages of WS* are multiple and have already achieved industrial impact. WS* descriptions are exchangeable and developers may use different implementations for the same Web Service description. The disadvantages of WS*, however, are also apparent: even though the different standards are complementary, they must overlap and one may produce models composed of different WS* descriptions, which are inconsistent with each other, but the reasons for the inconsistencies are not easily determined. This is the case because there is no coherent conceptual model of WS*, i.e. terms with equivalent semantics are introduced differently in the respective XML-DTDs. Thus, it is impossible to ask for conclusions that come from integrating different WS* descriptions. Hence, discovering such Web Service management problems or asking for other similar kinds of conclusions that derive from the integration of WS* descriptions remains a purely manual task to be done by the software developers accompanied by little to no formal machinery.
%I W3C Workshop on Frameworks for Semantics in Web Services
%G eng
%0 Journal Article
%J IEEE Intelligent Systems
%D 2005
%T The Semantic Web in One Day
%A York Sure
%A Andreas Eberhart
%A Rudi Studer
%A Pascal Hitzler
%K Semantic Web
%B IEEE Intelligent Systems
%P 85-87
%G eng
%0 Journal Article
%J Journal of Logic and Computation
%D 2005
%T Towards a Systematic Account of Different Semantics for Logic Programs
%A Pascal Hitzler
%K Kripke Kleene semantics
%K logic programming
%K programming semantics
%X In [1,2], a new methodology has been proposed which allows to derive uniform characterizations of different declarative semantics for logic programs and negation. One result from this work is that the well-founded semantics can formally be understood as a stratified version of Fitting (or Kripke Kleene) semantics. The construction leading to this result, however, show a certain asymmetry which is not readily understood. We will study this situation here with the result that we will obtain a coherent picture of relations between different semantics.
%B Journal of Logic and Computation
%P 391-404
%G eng
%0 Journal Article
%J Theory and Practice of Logic Programming
%D 2005
%T A uniform approach to logic programming semantics
%A Matthias Wendt
%A Pascal Hitzler
%K logic programming semantics
%X Part of the theory of programming and nonymonotonic reasoning concerns the study of fixed-point semantics for these paradigms. Several different semantics have been proposed during the last two decades, and some have been more successful and acknowledged than others. The rationales behind those various semantics have been manifold, depending on one's point of view, which may be that of a programmer or inspired by commonsense reasoning, and consequently the constructions which lead to these semantics are technically very diverse, and the exact relationships between them have not yet been fully understood. In this paper, we present a conceptually new method, based on level mappings, which allows to provide uniform characterizations of different semantics for logic programs. We will display our approach by giving new and uniform characterizations of some of the major semantics, and of the well-founded semantics. A novel characterization of the weakly perfect model semantics will also be provided.
%B Theory and Practice of Logic Programming
%P 123-159
%G eng
%0 Conference Paper
%B 8th International Conference, LPNMR 2005
%D 2005
%T The Well-Supported Semantics for Multidimensional Dynamic Logic Programs
%A F. Banti
%A Jose Julio Alferes
%A A. Brogi
%A Pascal Hitzler
%X Multidimensional dynamic logic programs are a paradigm which allows to express (partially) hierarchically ordered evolving knowledge bases through (partially) ordered multi sets of logic programs and allowing to solve contradictions among rules in different programs by allowing rules in more important programs to reject rules in less important ones. This class of programs extends the class of dynamic logic program that provides meaning and semantics to sequences of logic programs. Recently a semantics named refined stable model semantics has fixed some counterintuitive behaviour of previously existing semantics for dynamic logic programs. However, it is not possible to directly extend the definitions and concepts of the refined semantics to the multidimensional case and hence more sophisticated principles and techniques are in order. In this paper we face the problem of defining a proper semantics for multidimensional dynamic logic programs by extending the idea of well supported model to this class of programs and by showing that this concept alone is enough for univocally characterizing a proper semantics. We then show how the newly defined semantics coincides with the refined one when applied to sequences of programs.
%B 8th International Conference, LPNMR 2005
%C Diamante, Italy
%P 356-368
%G eng
%0 Conference Paper
%D 2005
%T What Is Ontology Merging? - A Category-Theoretical Perspective Using Pushouts
%A York Sure
%A Markus Krotzsch
%A Marc Ehrig
%A Pascal Hitzler
%X In this paper we explain how merging of ontologies is captured by the pushout construction from category theory, and argue that this is a very natural approach to the problem. We study this independent of a specific choice of ontology representation language, and thus provide a sort of blueprint for the development of algorithms applicable in practice. For this purpose, we view category theory as a universal 'meta specification language' that enables us to specify properties of ontological relationships and constructions in a way that does not depend on any particular implementation. This can be achieved since the basic objects of study in category theory are the relationships between multiple ontological specifications, not the internal structure of a single knowledge representation. Categorical pushouts are already considered in some approaches to ontology research (Jannink et al. 1998; Schorlemmer, Potter, & Robertson 2002; Goguen 2005; Kent 2005) and we do not claim our treatment to be entirely original. Still we have the impression that the potential of category theoretic approaches is by far not exhausted in todays ontology research. For our particular case the treatment will focus on the ontology merging, for which we will give both intuitive explanations and precise definitions. This reflects our belief that, at the current stage of research, it is not desirable to fade out the mathematical details of the categorical approach completely, since the interfaces to current techniques in ontology research are not yet available to their full extent. We will also keep this treatment rather general, not narrowing the discussion to specific formalisms - this added generality is one of the strengths of category theory. A long version of this paper with a tutorial character is available from the first author's homepage.
%I 20th National Conference on Artificial Intelligence, AAAI-05
%G eng
%0 Conference Paper
%B A cartesian closed category of approximable concept structures
%D 2004
%T A cartesian closed category of approximable concept structures
%A Guo-Qiang Zhang
%A Pascal Hitzler
%X Infinite contexts and their corresponding lattices are of theoretical and practical interest since they may offer connections with and insights from other mathematical structures which are normally not restricted to the finite cases. In this paper we establish a systematic connection between formal concept analysis and domain theory as a categorical equivalence, enriching the link between the two areas as outlined in [25]. Building on a new notion of approximable concept introduced by Zhang and Shen [26], this paper provides an appropriate notion of morphisms on formal contexts and shows that the resulting category is equivalent to (a) the category of complete algebraic lattices and Scott continuous functions, and (b) a category of information systems and approximable mappings. Since the latter categories are cartesian closed, we obtain a cartesian closed category of formal contexts that respects both the context structures as well as the intrinsic notion of approximable concepts at the same time.
%B A cartesian closed category of approximable concept structures
%G eng
%0 Conference Paper
%B Default Reasoning over Domains and Concept Hierarchies
%D 2004
%T Default Reasoning over Domains and Concept Hierarchies
%A Pascal Hitzler
%X W.C. Rounds and G.-Q. Zhang have proposed to study a form of disjunctive logic programming generalized to algebraic domains [1]. This system allows reasoning with information which is hierarchically structured and forms a (suitable) domain. We extend this framework to include reasoning with default negation, giving rise to a new nonmonotonic reasoning framework on hierarchical knowledge which encompasses answer set programming with extended disjunctive logic programs. We also show that the hierarchically structured knowledge on which programming in this paradigm can be done, arises very naturally from formal concept analysis. Together, we obtain a default reasoning paradigm for conceptual knowledge which is in accordance with mainstream developments in nonmonotonic reasoning.
%B Default Reasoning over Domains and Concept Hierarchies
%G eng
%0 Conference Paper
%B Third International Conference on Information
%D 2004
%T The Integration of Connectionism and First-Order Knowledge Representation and Reasoning as a Challenge for Artificial Intelligence
%A Sebastian Bader
%A Steffen Holldobler
%A Pascal Hitzler
%X Intelligent systems based on first-order logic on the one hand, and on artificial neural networks (also called connectionist systems) on the other, differ substantially. It would be very desirable to combine the robust neural networking machinery with symbolic knowledge representation and reasoning paradigms like logic programming in such a way that the strengths of either paradigm will be retained. Current state-of-the-art research, however, fails by far to achieve this ultimate goal. As one of the main obstacles to be overcome we perceive the question how symbolic knowledge can be encoded by means of connectionist systems: Satisfactory answers to this will naturally lead the way to knowledge extraction algorithms and to integrated neural-symbolic systems.
%B Third International Conference on Information
%C Tokyo, Japan
%G eng
%0 Generic
%D 2004
%T Level mapping characterizations of selector-generated models for logic programs
%A Sibylle Schwarz
%A Pascal Hitzler
%G eng
%0 Journal Article
%J Journal of Applied Logic
%D 2004
%T Logic Programs, Iterated Function Systems, and Recurrent Radial Basis Function Networks
%A Sebastian Bader
%A Pascal Hitzler
%K iterated functions
%X Graphs of the single-step operator for first-order logic programs -displayed in the real plane - exhibit self-similar structures known from topological dynamics, i.e. they appear to be *fractals*, or more precisely, attractors of iterated function systems. We show that this observation can be made mathematically precise. In particular, we give conditions which ensure that those graphs coincide with attractors of suitably chosen iterated function systems, and conditions which allow the approximation of such graphs by iterated function systems or by fractal interpolation. Since iterated function systems can easily be encoded using recurrent radial basis function networks, we eventually obtain connectionist systems which approximate logic programs in the presence of function symbols.
%B Journal of Applied Logic
%P 273- 300
%G eng
%0 Conference Paper
%B the 26th Annual German Conference on Artificial Intelligence, KI2003
%D 2003
%T Continuity of Semantic Operators in Logic Programming and their Approximation by Artificial Neural Networks.
%A Anthony K. Seda
%A Pascal Hitzler
%X One approach to integrating First-order logic programming and neural network systems employs the approximation of semantic operators by feedforward networks. For this purpose, it is necessary to view these semantic operators as continuous functions on the reals. This can be accomplished by endowing the space of all interpretations of a logic program with topologies obtained from suitable embeddings. We will present such topologies which arise naturally out of the theory of logic programming, discuss continuity issues of several wellknown semantic operators, and derive some results concerning the approximation of these operators by feedforward neural networks.
%B the 26th Annual German Conference on Artificial Intelligence, KI2003
%C Hamburg, Germany
%P 105-119
%G eng
%0 Conference Paper
%B ICCS 2003
%D 2003
%T Formal Concept Analysis and Resolution in Algebraic Domains
%A Matthias Wendt
%A Pascal Hitzler
%X We relate two formerly independent areas: Formal concept analysis and logic of domains. We will establish a correspondene between contextual attribute logic on formal contexts resp. concept lattices and a clausal logic on coherent algebraic cpos. We show how to identify the notion of formal concept in the domain theoretic setting. In particular, we show that a special instance of the resolution rule from the domain logic coincides with the concept closure operator from formal concept analysis. The results shed light on the use of contexts and domains for knowledge representation and reasoning purposes.
%B ICCS 2003
%C Shaker Verlag, Aachen
%P 205-221
%G eng
%0 Generic
%D 2003
%T Formal Concept Analysis and Resolution on Algebraic Domains - Preliminary Report
%A Matthias Wendt
%A Pascal Hitzler
%X We relate two formerly independent areas: Formal concept analysis and logic of domains. We will establish a correspondene between contextual attribute logic on formal contexts resp. concept lattices and a clausal logic on coherent algebraic cpos. We show how to identify the notion of formal concept in the domain theoretic setting. In particular, we show that a special instance of the resolution rule from the domain logic coincides with the concept closure operator from formal concept analysis. The results shed light on the use of contexts and domains for knowledge representation and reasoning purposes.
%G eng
%0 Journal Article
%J Theoretical Computer Science
%D 2003
%T Generalized Metrics and Uniquely Determined Logic Programs
%A Anthony K. Seda
%A Pascal Hitzler
%K Priess-Crampe and Ribenboim Fixed-Point Theorem
%K Ultrametrics
%X The introduction of negation into logic programming brings the benefit of enhanced syntax and expressibility, but creates some semantical problems. Specifically, certain operators which are monotonic in the absence of negation become non-monotonic when it is introduced, with the result that standard approaches to denotational semantics then become inapplicable. In this paper, we show how generalized metric spaces can be used to obtain fixed-point semantics for several classes of programs relative tot eh supported model semantics, and investigate relationships between the underlying spaces we employ. Our methods allow the analysis of classes of programs which include the acyclic, locally hierarchical, and acceptable programs amongst others, and draw on fixed-point theorems which apply to generalized ultrametric spaces and to partial metric spaces.
%B Theoretical Computer Science
%P 187-219
%G eng
%0 Conference Paper
%B IJCAI-03
%D 2003
%T A Resolution Theorem for Algebraic Domains
%A Pascal Hitzler
%X W. C. Rounds and G.-Q. Zhang have recently proposed to study a form of resolution on algebraic domains [Rounds and Zhang, 2001]. This framework allows reasoning with knowledge which is hierarchically structured and forms a (suitable) domain, more precisely, a coherent algebraic cpo as studied in domain theory. In this paper, we give conditions under which a resolution theorem -- in a form underlying resolution-based logic programming systems -- can be obtained. The investigations bear potential for engineering new knowledge representation and reasoning systems on a firm domain-theoretic background.
%B IJCAI-03
%C Acapulco, Mexico
%P 1339-1340
%G eng
%0 Conference Paper
%B 26th Annual German Conference on Artificial Intelligence, KI2003
%D 2003
%T Towards a Systematic Account of Different Logic Programming Semantics
%A Pascal Hitzler
%X In [14, 15], a new methodology has been proposed which allows to derive uniform characterizations of different declarative semantics for logic programs with negation. One result from this work is that the well-founded semantics can formally be understood as a stratiÃ¯Â¬Âed version of the Fitting (or Kripke-Kleene) semantics. The constructions leading to this result, however, show a certain asymmetry which is not readily understood. We will study this situation here with the result that we will obtain a coherent picture of relations between different semantics for normal logic programs.
%B 26th Annual German Conference on Artificial Intelligence, KI2003
%C Hamburg, Germany
%P 355-369
%G eng
%0 Conference Paper
%D 2002
%T Characterizing Logic Programming Semantics with Level Mappings
%A Matthias Wendt
%A Pascal Hitzler
%X Declarative semantics in logic programming and nonmonotonic reasoning are often defined via fixed points of semantic operators. While many relationships between different semantics known from the literature have been studied, a uniform treatment is still missing. In this paper, we provide uniform operator-free characterizations for some of the most important semantics, more precisely, for the stable, the well-founded, and the Fitting semantics, for the weakly-perfect model semantics, and for the least model semantics for negation-free programs.
%I WLP: Workshop Logische Programmierung
%G eng
%0 Generic
%D 2002
%T Contexts, Concepts, and Logic of Domains
%A Pascal Hitzler
%G eng
%0 Book Section
%D 2002
%T The Fixed-Point Theorems of Priess-Crampe and Ribenboim in Logic Programming
%A Anthony K. Seda
%A Pascal Hitzler
%G eng
%0 Journal Article
%J Technische Berichte Technical Reports
%D 2002
%T ILP Operators for Propositional Connectionist Networks
%A Miguel Gutierrez-Naranjo
%A Pascal Hitzler
%B Technische Berichte Technical Reports
%C WLP: Workshop Logische Programmierung
%P 103-106
%G eng
%0 Conference Paper
%D 2002
%T Towards Nonmonotonic Reasoning on Hierarchical Knowledge
%A Pascal Hitzler
%K nonmonotonic reasoning and hierarchial knowledge
%X W.C. Rounds and G.Q. Zhang have recently proposed to study a form of disjunctive logic programming generalized to algebraic domains [RZ01]. This system allows reasoning with information which is hierarchically structured and forms a (suitable) domain. We extend this framework to include reasoning with negative information, i.e. the implicit or explicit absence of bits of information. These investigations will naturally lead to a form of default reasoning which is strongly related to programming with answer sets to stable models, which has recently created much interest amongst artificial intelligence researchers concerned with knowledge representation and reasoning.
%I WLP: Workshop Logische Programmierung
%G eng
%0 Conference Paper
%B The Well-Founded Semantics is a Stratified Fitting Semantics
%D 2002
%T The Well-Founded Semantics is a Stratified Fitting Semantics
%A Matthias Wendt
%A Pascal Hitzler
%X Part of the theory of logic programming and nonmonotonic reasoning concerns the study of fixed-point semantics for these paradigms. While several different semantics have been proposed, and some have been more successful than others, the exact relationships between the approaches have not yet been fully understood. In this paper, we give new characterizations, using level mappings, of the Fitting semantics, the well-founded semantics, and the weakly perfect model semantics. The results will unmask the well-founded semantics as a stratified version of the Fitting semantics.
%B The Well-Founded Semantics is a Stratified Fitting Semantics
%G eng
%0 Journal Article
%J Journal of Electrical Engineering
%D 2001
%T A "Converse" of the Bananch Contraction Mapping Theorem
%A Pascal Hitzler
%A Anthony K. Seda
%K Banach contraction
%K Banach contraction mapping theorem
%X We prove a type of converse of the Banach contraction mapping theorem for metric spaces: if X is a T_{1} topological space and *f*: X -> X is a function with the unique fixed point *a* such that *f*^{n}(*x*) converges to *a* for each *x* is a member of *X*, then there exists a distance function *d* on *X* such that *f* is a contraction on the complete ultrametric space (X,d) with contractivity factor 1/2. We explore properties of the resulting space (X,d).
%B Journal of Electrical Engineering
%P 3-6
%G eng
%0 Book Section
%D 2001
%T Kontraktionssatze auf verallgemeinerten metrischen Raumen
%A Pascal Hitzler
%G eng
%0 Conference Paper
%B 7th International Conference on Information Systems Analysis and Synthesis (ISAS 2001)
%D 2001
%T Semantic Operators and Fixed-Point Theory in Logic Programming
%A Anthony K. Seda
%A Pascal Hitzler
%X We consider rather general operators mapping valuations to (sets of) valuations in the context of the semantics of logic programming languages. This notion generalizes several of the standard operators encountered in this subject and is inspired by earlier work of M.C. Fitting. The fixed points of such operators play a fundamental role in logic programming semantics by providing standard models of logic programs and also in determining the computability properties of these standard models. We discuss some of our recent work employing topological ideas, in conjunction with order theory, to establish methods by which one can nd the fixed points of the operators arising in logic programming semantics.
%B 7th International Conference on Information Systems Analysis and Synthesis (ISAS 2001)
%C Orlando, Florida, USA
%P 224-229
%G eng
%0 Journal Article
%J Information
%D 2001
%T Unique Supported-Model Classes of Logic Programs
%A Anthony K. Seda
%A Pascal Hitzler
%K denotational semantics
%K logic programming
%K supported-model semantics
%X We study classes of programs, herein called *unique supported-model classes,* with the property that each program in the class has a unique supported model. Elsewhere, the authors examined these classes from the point of view of operators defined relative to certain three-valued logics. In this paper, we complement our earlier results by considering how unique supported-model classes fit into the framework given by various classes of programs in several well-known approaches to semantics.
%B Information
%P 295-302
%G eng
%0 Conference Paper
%D 2001
%T VDM meets LCF: Domain-Theoretic and Topological Aspects of VDM
%A Anthony Seda
%A Pascal Hitzler
%I Fifth Irish Workshop on Formal Methods (IWFM'01)
%G eng
%0 Conference Paper
%B Classes of Logic Programs which Possess Unique Supported Models.
%D 2000
%T Classes of Logic Programs which Possess Unique Supported Models.
%A Anthony K. Seda
%A Pascal Hitzler
%X Logic programming is concerned with the use of logic as a programming language. The main manifestation of this computing paradigm is in the various versions of Prolog which are now available, in which computation is viewed as deduction from sets of Horn clauses, although there is also growing interest in the related form known as answer set programming, see [10]. The reference [1] contains a good survey of the growth of logic programming over the last twenty-five years both as a stand-alone programming language and as a software component of large information systems. One advantage a logic program P has over conventional imperative and object oriented programs is that it has a natural machine-independent meaning, namely, its logical meaning. This is often referred to as its declarative semantics, and is usually taken to be some 'standard' model canonically associated with P. Unfortunately, it is often the case that there are many possible choices for the standard model, some even taken in many-valued logic, which do not in general coincide and all of which have a claim to be 'the natural choice' depending on one's view of non-monotonic reasoning [6, 7, 11].
%B Classes of Logic Programs which Possess Unique Supported Models.
%G eng
%0 Conference Paper
%B On the Coincidence of Semantics for Uniquely Determined Programs
%D 2000
%T On the Coincidence of Semantics for Uniquely Determined Programs
%A Anthony K. Seda
%A Pascal Hitzler
%X We study classes of logic programs, called here unique supported model classes or simply usm- classes, with the property that each member in the class is uniquely determined, that is, possesses a unique supported model. Known classes of uniquely determined programs include the acyclic and the acceptable programs, which have been much studied in the context of termination, and the authors gave a unifying treatment of these and other unique supported model classes in an earlier paper. In the present paper, we complement these earlier results by considering how various standard semantics relate to each other within certain unique supported model classes. In particular, we introduce the natural usm-class of all accessible programs, which contains the aforementioned classes, and has the property that, for each member of it, the stable, well-founded and weakly perfect-a models all coincide.
%B On the Coincidence of Semantics for Uniquely Determined Programs
%G eng
%0 Book Section
%D 2000
%T Der Banachsche Fixpunktsatz und der Satz von Picard-Lindelof
%A Frithjof Lutscher
%A Pascal Hitzler
%G eng
%0 Journal Article
%D 2000
%T Dislocated Topologies
%A Pascal Hitzler
%A Anthony K. Seda
%K Banach contraction
%K topologies
%X We study a generalized notion of topology which evolved out of applications in the area of logic programming semantics. The generalization is obtained by relaxing the requirements that a neighbourhood of a point includes the point itself, and by allowing neighbourhoods of points to be empty. The correspoding generalized notion of metric is obtained by allowing points to have non-zero distance to themselves. We further show that it is meaningful to discuss neightbourhoods, convergence, and continuity in these spaces. A generalized version of the Banach contraction mapping theorem can also be established. We show finally how the generalized metrics studied here can be obtained from conventional metrics.
%G eng
%0 Generic
%D 2000
%T Dislocated Topologies
%A Pascal Hitzler
%A Anthony Seda
%A Anthony K. Seda
%X We study a generalized notion of topology which evolved out of applications in the area of logic programming semantics. The generalization is obtained by relaxing the requirements that a neighbourhood of a point includes the point itself, and by allowing neighbourhoods of points to be empty. The correspoding generalized notion of metric is obtained by allowing points to have non-zero distance to themselves. We further show that it is meaningful to discuss neightbourhoods, convergence, and continuity in these spaces. A generalized version of the Banach contraction mapping theorem can also be established. We show finally how the generalized metrics studied here can be obtained from conventional metrics.
%G eng
%0 Conference Paper
%B SCI2000 and ISAS2000
%D 2000
%T A New Fixed-point Theorem for Logic Programming Semantics
%A Anthony K. Seda
%A Pascal Hitzler
%X We present a new fixed-point theorem akin to the Banach contraction mapping theorem, but in the context of a novel notion of generalized metric space, and show how it can be applied to analyse the denotational semantics of certain logic programs. The theorem is obtained by generalizing a theorem of Priess-Crampe and Ribenboim, which grew out of applications within valuation theory, but is also inspired by a theorem of S.G. Matthews which grew out of applications to conventional programming language semantics. The class of programs to which we apply our theorem was defined previously by us in terms of operators using three-valued logics. However, the new treatment we provide here is short and intuitive, and provides further evidence that metriclike structures are an appropriate setting for the study of logic programming semantics.
%B SCI2000 and ISAS2000
%C Orlando, Florida, USA
%P 418-423
%G eng
%0 Generic
%D 2000
%T A Topological View of Acceptability
%A Anthony K. Seda
%A Pascal Hitzler
%G eng
%0 Conference Paper
%D 1999
%T Acceptable Programs Revisited
%A Anthony K. Seda
%A Pascal Hitzler
%K l and o and g and i and c and and p and r and o and g and r and a and m and s
%X Acceptable logic programs have been studied extensively in the context of proving termination of Prolog programs. It is difficult, however, to establish acceptability from the definition since this depends on finding a suitable model, which need not be a Herbrand model in general, together with a suitable level mapping that one can use to check the conditions which characterize acceptability. In this paper, we will see that when working over a fixed but arbitrary preinterpretation, a method can be provided for obtaining both a suitable model and a canonical level mapping which are sufficient for this purpose. Furthermore, the canonical model and level mapping obtained will turn out to be sufficient for discussing termination of non-ground queries.
%I Workshop on Verification in Logic Programming, 16th International Conference on Logic Programming (ICLP'99),
%G eng
%0 Conference Paper
%B A Characterization of Acceptability
%D 1999
%T A Characterization of Acceptability
%A Anthony K. Seda
%A Pascal Hitzler
%B A Characterization of Acceptability
%G eng
%0 Conference Paper
%B Characterizations of Classes of Programs by Three-valued Operators
%D 1999
%T Characterizations of Classes of Programs by Three-valued Operators
%A Anthony K. Seda
%A Pascal Hitzler
%X Several important classes of normal logic programs, including the classes of acyclic, acceptable, and locally hierarchical programs, have the property that every program in the class has a unique twovalued supported model. In this paper, we call such classes unique supported model classes. We analyse and characterize these classes by means of operators on three-valued logics. Our studies will motivate the definition of a larger unique supported model class which we call the class of Phi-accessible programs. Finally, we show that the class of Phi -accessible programs is computationally adequate in that every partial recursive function can be implemented by such a program.
%B Characterizations of Classes of Programs by Three-valued Operators
%G eng
%0 Conference Paper
%D 1999
%T Multivalued Mappings, Fixed-Point Theorems and Disjunctive Databases
%A Anthony K. Seda
%A Pascal Hitzler
%X In this paper, we discuss the semantics of disjunctive programs and databases and show how multivalued mappings and their fixed points arise naturally within this context. A number of fixed-point theorems for multivalued mappings are considered, some of which are already known and some of which are new. The notion of a normal derivative of a disjunctive program is introduced. Normal derivatives are normal logic programs which are determined by the disjunctive program. Thus, the well-known single-step operator associated with a normal derivative is single-valued, and its fixed points can be found by well-established means. It is shown how fixed points of the multivalued mapping determined by a disjunctive program relate to the fixed points of the single-step operators coming from its normal derivatives. This procedure has potential for simplifying the construction of models of disjunctive databases, and this point is discussed. Most of the results for multivalued mappings rest on corresponding, known results concerning fixed points of single-valued mappings. Since the latter results are frequently referred to, they have been collected together for convenience in a survey which should be of independent interest as well as being preparatory for the later results. Finally, a number of problems and issues raised by this work are discussed.
%I Electronic Workshops in Computing, British Computer Society
%G eng
%0 Journal Article
%J Topology Proceedings
%D 1999
%T Some Issues Concerning Fixed-Points in Computational Logic: Quasi-Metrics, Multivalued Mappings and the Knaster-Tarski Theorem
%A Anthony K. Seda
%A Pascal Hitzler
%K fixed points
%K Knaster Tarski and Kleene theorems
%K multivalued mappings
%X Many questions concerning the semantics of disjunctive databases and of logic programming systems depend on the fixed points of various multivalued mappings and operations determined by the database or program. We discuss known versions for multivalued mappings of the Knaster-Tarski theorem and of the Banach contraction mapping theorem and formulate a version of the classical fixed point theorem (sometimes attributed to Kleene) which is new. All these results have applications to the semantics of disjunctive logic programs, and we will describe a class of programs to which the new theorem can be applied. We also show that a unification of the latter two theorems is possible, using quasi-metrics, which parallels the well-known unification of Rutten and Smyth in the case of conventional programming language semantics.
%B Topology Proceedings
%P 223-250
%G eng
%0 Conference Paper
%D 1998
%T Strictly Level-Decreasing Logic Programs
%A Anthony K. Seda
%A Pascal Hitzler
%X We study strictly level-decreasing logic programs (sld-programs) as defined earlier by the present authors. It will be seen that sld-programs, unlike most other classes of logic programs, have both a highly intuitive declarative semantics, given as a unique supported model, and are computationally adequate in the sense that every partial recursive function can be represented by some sld-program *P*. Allowing for a safe use of cuts, an interpreter based on SLDNF-resolution, as implemented for example in standard Prolog systems, is shown to be sound and complete with respect to this class of programs. Furthermore, we study connections between topological dynamics and logic programming which are suggested by our approach to the declarative semantics of sld-programs.
%I the Second Irish Workshop on Formal Methods
%G eng
%0 Book Section
%D 1997
%T Der Kontraktionssatz auf metrischen Raumen
%A Pascal Hitzler
%G eng
%0 Book Section
%D 1997
%T Fixpunktsemantik
%A M. Grimm
%A G. Kalmbach
%A Pascal Hitzler
%G eng
%0 Generic
%D 1997
%T Sur les programmes logiques localement stratifiés
%A Anthony Seda
%A Pascal Hitzler
%G eng
%0 Book Section
%D 1996
%T Spieltheorie
%A Alexander Chocholaty
%A Pascal Hitzler
%G eng