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36
Query Answering for OWLDL with Rules
 Journal of Web Semantics
, 2004
"... Both OWLDL and functionfree Horn rules are decidable fragments of firstorder logic with interesting, yet orthogonal expressive power. A combination of OWLDL and rules is desirable for the Semantic Web; however, it might easily lead to the undecidability of interesting reasoning problems. Here, w ..."
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Cited by 329 (28 self)
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Both OWLDL and functionfree Horn rules are decidable fragments of firstorder logic with interesting, yet orthogonal expressive power. A combination of OWLDL and rules is desirable for the Semantic Web; however, it might easily lead to the undecidability of interesting reasoning problems. Here, we present a decidable such combination where rules are required to be DLsafe: each variable in the rule is required to occur in a nonDLatom in the rule body. We discuss the expressive power of such a combination and present an algorithm for query answering in the related logic SHIQ extended with DLsafe rules, based on a reduction to disjunctive programs.
On the Properties of Metamodeling in OWL
 In 4th Int. Semantic Web Conf. (ISWC 2005
, 2005
"... Abstract. A common practice in conceptual modeling is to separate the intensional from the extensional model. Although very intuitive, this approach is inadequate for many complex domains, where the borderline between the two models is not clearcut. Therefore, OWLFull, the most expressive of the S ..."
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Cited by 52 (0 self)
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Abstract. A common practice in conceptual modeling is to separate the intensional from the extensional model. Although very intuitive, this approach is inadequate for many complex domains, where the borderline between the two models is not clearcut. Therefore, OWLFull, the most expressive of the Semantic Web ontology languages, allows combining the intensional and the extensional model by a feature we refer to as metamodeling. In this paper, we show that the semantics of metamodeling adopted in OWLFull leads to undecidability of basic inference problems, due to free mixing of logical and metalogical symbols. Based on this result, we propose two alternative semantics for metamodeling: the contextual and the HiLog semantics. We show that SHOIQ — a description logic underlying OWLDL — extended with metamodeling under either semantics is decidable. Finally, we show how the latter semantics can be used in practice to axiomatize the logical interaction between concepts and metaconcepts. 1
Probabilistic description logic programs
, 2006
"... Towards sophisticated representation and reasoning techniques that allow for probabilistic uncertainty in the Rules, Logic, and Proof layers of the Semantic Web, we present probabilistic description logic programs (or pdlprograms), which are a combination of description logic programs (or dlprog ..."
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Cited by 43 (15 self)
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Towards sophisticated representation and reasoning techniques that allow for probabilistic uncertainty in the Rules, Logic, and Proof layers of the Semantic Web, we present probabilistic description logic programs (or pdlprograms), which are a combination of description logic programs (or dlprograms) under the answer set semantics and the wellfounded semantics with Poole’s independent choice logic. We show that query processing in such pdlprograms can be reduced to computing all answer sets of dlprograms and solving linear optimization problems, and to computing the wellfounded model of dlprograms, respectively. Moreover, we show that the answer set semantics of pdlprograms is a refinement of the wellfounded semantics of pdlprograms. Furthermore, we also present an algorithm for query processing in the special case of stratified pdlprograms, which is based on a reduction to computing the canonical model of stratified dlprograms.
A Decomposition Rule for Decision Procedures by Resolutionbased Calculi
 In: Proc. 11th Int. Conf. on Logic for Programming, Artificial Intelligence, and Reasoning (LPAR
, 2004
"... Abstract. Resolutionbased calculi are among the most widely used calculi for theorem proving in firstorder logic. Numerous refinements of resolution are nowadays available, such as e.g. basic superposition, a calculus highly optimized for theorem proving with equality. However, even such an advanc ..."
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Cited by 36 (11 self)
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Abstract. Resolutionbased calculi are among the most widely used calculi for theorem proving in firstorder logic. Numerous refinements of resolution are nowadays available, such as e.g. basic superposition, a calculus highly optimized for theorem proving with equality. However, even such an advanced calculus does not restrict inferences enough to obtain decision procedures for complex logics, such as SHIQ. In this paper, we present a new decomposition inference rule, which can be combined with any resolutionbased calculus compatible with the standard notion of redundancy. We combine decomposition with basic superposition to obtain three new decision procedures: (i) for the description logic SHIQ, (ii) for the description logic ALCHIQb, and (iii) for answering conjunctive queries over SHIQ knowledge bases. The first two procedures are worstcase optimal and, based on the vast experience in building efficient theorem provers, we expect them to be suitable for practical usage. 1
Resolutionbased approximate reasoning for OWL DL
 PROC. ISWC2005
, 2005
"... We propose a new technique for approximate ABox reasoning with OWL DL ontologies. Essentially, we obtain substantially improved reasoning performance by disregarding nonHorn features of OWL DL. Our approach comes as a sideproduct of recent research results concerning a new transformation of OWL D ..."
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Cited by 36 (10 self)
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We propose a new technique for approximate ABox reasoning with OWL DL ontologies. Essentially, we obtain substantially improved reasoning performance by disregarding nonHorn features of OWL DL. Our approach comes as a sideproduct of recent research results concerning a new transformation of OWL DL ontologies into negationfree 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 nondisjunctive ones. We analyse our reasoning approach by means of nonmonotonic reasoning techniques, and present an implementation, called Screech.
A Mapping System for the Integration Of OwlDl Ontologies
 IN IN PROCEEDINGS OF THE ACMWORKSHOP: INTEROPERABILITY OF HETEROGENEOUS INFORMATION SYSTEMS (IHIS05
, 2005
"... To enable interoperability between applications in distributed information systems based on heterogeneous ontologies, it is necessary to formally define the notion of a mapping between ontologies. In this paper, we define a mapping system for OWLDL ontologies, where mappings are expressed as corre ..."
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Cited by 34 (3 self)
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To enable interoperability between applications in distributed information systems based on heterogeneous ontologies, it is necessary to formally define the notion of a mapping between ontologies. In this paper, we define a mapping system for OWLDL ontologies, where mappings are expressed as correspondences between conjunctive queries over ontologies. As query answering within such a general mapping system is undecidable, we identify a decidable fragment of the mapping system, which corresponds to OWLDL extended with DLsafe rules. We further show how the mapping system can be applied for the task of ontology integration and present a query answering algorithm.
Logical reconstruction of normative RDF
 In OWL: Experiences and Directions Workshop (OWLED2005
, 2005
"... Abstract. In this sketchy paper we introduce a logical reconstruction of the RDF family of languages and the OWLDL family of languages. We prove that our logical framework is equivalent to the normative W3C definitions of RDF/RDFS and OWLDL/Lite. The main aim is to have a unified model theoretic s ..."
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Cited by 30 (6 self)
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Abstract. In this sketchy paper we introduce a logical reconstruction of the RDF family of languages and the OWLDL family of languages. We prove that our logical framework is equivalent to the normative W3C definitions of RDF/RDFS and OWLDL/Lite. The main aim is to have a unified model theoretic semantics for both worlds. As a consequence we get various complexity results and a model theoretic semantics for basic SPARQL. 1
dlpconvert  Converting OWL DLP statements to logic programs
 In: European Semantic Web Conference 2005 Demos and Posters
, 2005
"... this document, dlpconvert is still in a beta version and quite a number of features are waiting to be implemented. This includes minor changes like adding more sophisticated error messages and switches for the website version. More substantially, we intend to provide an FLogic serialization for the ..."
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Cited by 11 (3 self)
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this document, dlpconvert is still in a beta version and quite a number of features are waiting to be implemented. This includes minor changes like adding more sophisticated error messages and switches for the website version. More substantially, we intend to provide an FLogic serialization for the output in order to facilitate interoperability with FLogic based systems like Ontobroker, and thereby an integration of OWL DLP into FLogic reasoners. We also intend to improve the implemented heuristics for generating names and consider namespaces in order to avoid clashes
Efficient Description Logic Reasoning in Prolog: The DLog system
 THEORY AND PRACTICE OF LOGIC PROGRAMMING
, 2009
"... Traditional algorithms for description logic (DL) instance retrieval are inefficient for large amounts of underlying data. As description logic is becoming popular in areas such as the Semantic Web and information integration, it is very important to have systems that can reason efficiently over lar ..."
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Cited by 10 (3 self)
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Traditional algorithms for description logic (DL) instance retrieval are inefficient for large amounts of underlying data. As description logic is becoming popular in areas such as the Semantic Web and information integration, it is very important to have systems that can reason efficiently over large data sets. In this paper we present an approach to transform description logic axioms described in the SHIQ DL language into a Prolog program. This transformation is done without any knowledge on the particular individuals: they are accessed dynamically during the normal Prolog execution of the generated program. This technique, together with the topdown Prolog execution, implies that only those pieces of data are accessed which are indeed important for answering the query. This allows us to store the individuals in a database instead of memory, which results in better scalability and helps using description logic ontologies directly on top of existing information sources. The transformation process consists of two steps: (1) first we create FOL clauses of restricted form from the DL axioms, (2) then we generate a Prolog program from these. Step (2), which is the focus of the present paper, actually works on more general clauses than those obtainable by applying step (1) to a $\mathcal{SHIQ}$ knowledge base. We first present a base transformation, the output of which can be either executed using a simple interpreter or further extended to executable Prolog code. We then discuss several optimisation techniques, applicable to the output of the base transformation. Some of these techniques are specific to our approach, while others are general enough to be interesting for DL reasoner implementors not using Prolog. We give an overview of DLog, a DL reasoner in Prolog, which is an implementation of the techniques outlined above. We evaluate the performance of DLog and compare it to some widely used DL reasoners, such as RacerPro, Pellet and KAON2.
Description logic programs: A practical choice for the modelling of ontologies
 IN 1ST WS ON FORMAL ONTOLOGIES MEET INDUSTRY, FOMI’05
, 2005
"... Knowledge representation using ontologies constitutes the heart of semantic technologies. Despite successful standardization efforts by the W3C, however, there are still numerous different ontology representation languages being used, and interoperability between them is in general not given. The pr ..."
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Cited by 5 (2 self)
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Knowledge representation using ontologies constitutes the heart of semantic technologies. Despite successful standardization efforts by the W3C, however, there are still numerous different 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 wellknown 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.