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Tractable Query Answering and Rewriting under Description Logic Constraints
 Journal of Applied Logic
"... Abstract. Answering queries over an incomplete database w.r.t. a set of constraints is an important computational task with applications in fields as diverse as information integration and metadata management in the Semantic Web. Description Logics (DL) are constraint languages that have been extens ..."
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Abstract. Answering queries over an incomplete database w.r.t. a set of constraints is an important computational task with applications in fields as diverse as information integration and metadata management in the Semantic Web. Description Logics (DL) are constraint languages that have been extensively studied in the past with the goal of providing useful modeling constructs while keeping the query answering problem decidable. For many DLs, query answering under constraints can be reduced to query rewriting: given a conjunctive query Q and a set of DL constraints T, the query Q can be transformed into a datalog query QT that takes into account the semantic consequences of T; then, to obtain answers to Q w.r.t. T and some (arbitrary) database instance A, one can simply evaluate QT over A using existing (deductive) database technology, without taking T into account. In this paper, we present a novel query rewriting algorithm that handles constraints modeled in the DL ELHIO ¬ and use it to show that answering conjunctive queries in this setting is PTimecomplete w.r.t. data complexity. Our algorithm deals with various description logics of the EL and DLLite families and is worstcase optimal w.r.t. data complexity for all of them. 1
High performance query answering over dllite ontologies
, 2012
"... Current techniques for query answering over DLLite ontologies have severe limitations in practice, since they either produce complex queries that are inefficient during execution, or require expensive data preprocessing. In light of this, we present two complementary sets of results that aim at im ..."
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Cited by 50 (7 self)
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Current techniques for query answering over DLLite ontologies have severe limitations in practice, since they either produce complex queries that are inefficient during execution, or require expensive data preprocessing. In light of this, we present two complementary sets of results that aim at improving the overall peformance of query answering systems. We show how to create ABox repositories that are complete w.r.t. a significant portion of DLLite TBoxes, including those expressed in RDFS, but where the data is not explicitly expanded. Second, we show how to characterize ABox completeness by means of dependencies, and how to use these and equivalence to optimize DLLite TBoxes. These results allow us to reduce the cost of query rewriting, often dramatically, and to generate highly efficient queries. We have implemented a novel system for query answering over DLLite ontologies that incorporates these techniques, and we present a series of dataintensive evaluations that show their effectiveness. 1
A FirstOrder Logic DavisPutnamLogemannLoveland Procedure
"... The DavisPutnamLogemannLoveland procedure (DPLL) was introduced in the early ..."
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Cited by 37 (6 self)
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The DavisPutnamLogemannLoveland procedure (DPLL) was introduced in the early
A resolutionbased decision procedure for SHOIQ
 Proc. of the 3rd Int. Joint Conf. on Automated Reasoning (IJCAR 2006), volume 4130 of LNAI
, 2006
"... Abstract. We present a resolutionbased decision procedure for the description logic SHOIQ—the logic underlying the Semantic Web ontology language OWLDL. Our procedure is goaloriented, and it naturally extends a similar procedure for SHIQ, which has proven itself in practice. Applying existing tec ..."
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Abstract. We present a resolutionbased decision procedure for the description logic SHOIQ—the logic underlying the Semantic Web ontology language OWLDL. Our procedure is goaloriented, and it naturally extends a similar procedure for SHIQ, which has proven itself in practice. Applying existing techniques for deriving saturationbased decision procedures to SHOIQ is not straightforward due to nominals, number restrictions, and inverse roles—a combination known to cause termination problems. We overcome this difficulty by using the basic superposition calculus, extended with custom simplification rules. 1
Decision Procedures using Model Building techniques
 In Computer Science Logic (9th Int. Workshop CSL'95
, 1996
"... . Few year ago we have developed an Automated Deduction approach to model building. The method, called RAMC 1 looks simultaneously for inconsistencies and models for a given formula. The capabilities of RAMC have been extended both for model building and for unsatisfiability detection by including ..."
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. Few year ago we have developed an Automated Deduction approach to model building. The method, called RAMC 1 looks simultaneously for inconsistencies and models for a given formula. The capabilities of RAMC have been extended both for model building and for unsatisfiability detection by including in it the use of semantic strategies. In the present work we go further in this direction and define more general and powerful semantic rules. These rules are an extension of Slagle 's semantic resolution. The robustness of our approach is evidenced by proving that the method is also a decision procedure for a wide range of classes decidable by semantic resolution and in particular by hyperresolution. Moreover, the method builds models for satisfiable formulae in these classes, in particular, for satisfiable formulae that do not have any finite model. 1 Introduction Model building and model checking are extremely important topics in Logic and Computer Science. Few years ago we have develop...
Resolution Methods for Decision Problems and FiniteModel Building
, 1992
"... Contents 1 Introduction 3 1.1 Related work : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 4 1.2 Structure of the thesis : : : : : : : : : : : : : : : : : : : : : : : : : : 4 2 Terminology 6 2.1 Terms, literals and clauses : : : : : : : : : : : : : : : : : : : : : : : : 6 2.2 Term s ..."
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Cited by 17 (1 self)
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Contents 1 Introduction 3 1.1 Related work : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 4 1.2 Structure of the thesis : : : : : : : : : : : : : : : : : : : : : : : : : : 4 2 Terminology 6 2.1 Terms, literals and clauses : : : : : : : : : : : : : : : : : : : : : : : : 6 2.2 Term structure and substitutions : : : : : : : : : : : : : : : : : : : : 7 2.3 Subsumption, factors, resolvents, splitting : : : : : : : : : : : : : : : 10 2.4 Herbrand semantics : : : : : : : : : : : : : : : : : : : : : : : : : : : : 12 2.5 Ordinary predicate logic and naming conventions : : : : : : : : : : : 12 3 Completeness of ordering refinements 14 3.1 Proving completeness by lifting : : : : : : : : : : : : : : : : : : : : 15 3.2 Some properties of 'Ø'predicates : : : : : : : : : : : : : : :
Computational Representations of Herbrand Models Using Grammars
 Computer Science Logic, 10th International Workshop, CSL'96, volume 1258 of LNCS
, 1997
"... . Finding computationally valuable representations of models of predicate logic formulas is an important subtask in many fields related to automated theorem proving, e.g. automated model building or semantic resolution. In this article we investigate the use of contextfree languages for representin ..."
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Cited by 9 (4 self)
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. Finding computationally valuable representations of models of predicate logic formulas is an important subtask in many fields related to automated theorem proving, e.g. automated model building or semantic resolution. In this article we investigate the use of contextfree languages for representing single Herbrand models, which appear to be a natural extension of "linear atomic representations" already known from the literature. We focus on their expressive power (which we find out to be exactly the finite models) and on algorithmic issues like clause evaluation and equivalence test (which we solve by using a resolution theorem prover), thus proving our approach to be an interesting base for investigating connections between formal language theory and automated theorem proving and model building. 1 Introduction Representing single models of predicate logic formulas plays an important role in various subfields of automated theorem proving. We just mention two of them: 1. An interesti...
Rewriting Conjunctive Queries over Description Logic Knowledge Bases
 In Proceedings of the International Workshop on Semantics in Data and Knowledge Bases
, 2008
"... Abstract. We consider the problems of conjunctive query answering and rewriting for information integration systems in which a Description Logic ontology is used to provide a global view of the data. We present a resolutionbased query rewriting algorithm for DLLite + ontologies, and use it to show ..."
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Abstract. We consider the problems of conjunctive query answering and rewriting for information integration systems in which a Description Logic ontology is used to provide a global view of the data. We present a resolutionbased query rewriting algorithm for DLLite + ontologies, and use it to show that query answering in this setting is NLogSpacecomplete with respect to data complexity. We also show that our algorithm produces an optimal rewriting when the input ontology is expressed in the language DLLite. Finally, we sketch an extended version of the algorithm that would, we are confident, be optimal for several DL languages with data complexity of query answering ranging from LogSpace to PTimecomplete. 1
Resolution Decides the Guarded Fragment
, 1998
"... We give resolution based decision procedures for the guarded fragment of ([ANB96]), and for the loosely guarded fragment of ([vBenthem97]). The relevance of the guarded fragments lies in the fact that many modal logics can be translated into them. In this way the guarded fragments act as a framework ..."
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Cited by 4 (0 self)
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We give resolution based decision procedures for the guarded fragment of ([ANB96]), and for the loosely guarded fragment of ([vBenthem97]). The relevance of the guarded fragments lies in the fact that many modal logics can be translated into them. In this way the guarded fragments act as a framework explaining the nice properties of these modal logics. By constructing an implementable decision procedure for the guarded fragments we define an effective procedure for deciding these modal logics. 1