Results 1 -
8 of
8
The Impact of Disjunction on Query Answering Under Guarded-based Existential Rules
"... Abstract. We give the complete picture of the complexity of conjunctive query answering under (weakly-)(frontier-)guarded disjunctive existential rules, i.e., existential rules extended with disjunction, and their main subclasses, linear rules and inclusion dependencies. 1 ..."
Abstract
-
Cited by 6 (3 self)
- Add to MetaCart
(Show Context)
Abstract. We give the complete picture of the complexity of conjunctive query answering under (weakly-)(frontier-)guarded disjunctive existential rules, i.e., existential rules extended with disjunction, and their main subclasses, linear rules and inclusion dependencies. 1
Pay-as-you-go Ontology Query Answering Using a Datalog Reasoner?
"... Abstract. We describe a hybrid approach to conjunctive query answer-ing over OWL 2 ontologies that combines a datalog reasoner with a fully-fledged OWL 2 reasoner in order to provide scalable “pay as you go ” performance. Our approach delegates the bulk of the computation to the highly scalable data ..."
Abstract
-
Cited by 2 (1 self)
- Add to MetaCart
(Show Context)
Abstract. We describe a hybrid approach to conjunctive query answer-ing over OWL 2 ontologies that combines a datalog reasoner with a fully-fledged OWL 2 reasoner in order to provide scalable “pay as you go ” performance. Our approach delegates the bulk of the computation to the highly scalable datalog engine and resorts to expensive OWL 2 reasoning only as necessary to fully answer the query. We have imple-mented a prototype system that uses RDFox as a datalog reasoner, and HermiT as an OWL 2 reasoner. Our evaluation over both benchmark and realistic ontologies and datasets suggests the feasibility of our approach. 1
Stable Model Semantics for Guarded Existential Rules and Description Logics
, 2014
"... We tackle a long-standing open research problem and prove the decidability of query answering under the stable model se-mantics for guarded existential rules, where rule bodies may contain negated atoms, and provide complexity results. The results extend to guarded Datalog ± with negation, and thus ..."
Abstract
-
Cited by 1 (0 self)
- Add to MetaCart
(Show Context)
We tackle a long-standing open research problem and prove the decidability of query answering under the stable model se-mantics for guarded existential rules, where rule bodies may contain negated atoms, and provide complexity results. The results extend to guarded Datalog ± with negation, and thus provide a natural and decidable stable model semantics to de-scription logics such as ELHI and DL-LiteR.
ASP Based Generation of Information Terms for Constructive EL
"... Abstract. Constructive description logics define interpretations of description logics under different constructive semantics. These logics have been mostly studied from the point of view of their formal properties: limited practical approaches have been shown for their use in knowledge representat ..."
Abstract
- Add to MetaCart
(Show Context)
Abstract. Constructive description logics define interpretations of description logics under different constructive semantics. These logics have been mostly studied from the point of view of their formal properties: limited practical approaches have been shown for their use in knowledge representation and Semantic Web languages and tools (which, on the other hand, constitute the distinctive applications of description logics). In this paper we demonstrate a solution to address this aspect: from the theoretical point of view, we first introduce an information terms semantics for the minimal description logic EL and we establish formal results linking this constructive semantics to answer set semantics. Using these results, on the practical side, we then present a prototype managing one aspect of such semantics (the generation of information terms of a knowledge base) using OWL-EL ontologies and "off the shelf" tools.
HEX-Programs with Existential Quantification?
"... Abstract. HEX-programs extend ASP by external sources. In this paper, we present domain-specific existential quantifiers on top of HEX-programs, i.e., ASP programs with external access which may introduce new values that also show up in the answer sets. Pure logical existential quantification corres ..."
Abstract
- Add to MetaCart
(Show Context)
Abstract. HEX-programs extend ASP by external sources. In this paper, we present domain-specific existential quantifiers on top of HEX-programs, i.e., ASP programs with external access which may introduce new values that also show up in the answer sets. Pure logical existential quantification corresponds to a specific instance of our approach. Programs with existential quantifiers may have infinite groundings in general, but for specific reasoning tasks a finite subset of the grounding can suffice. We introduce a generalized grounding algorithm for such problems, which exploits domain-specific termination criteria in order to generate a finite grounding for bounded model generation. As an application we consider query answering over existential rules. In contrast to other approaches, several extensions can be naturally integrated into our approach. We further show how terms with function symbols can be handled by HEX-programs, which in fact can be seen as a specific form of existential quantification. 1
Acyclic Query Answering Under Guarded Disjunctive Existential Rules and Consequences to DLs
"... The complete picture of the complexity of conjunctive query answer-ing under guarded disjunctive existential rules has been recently settled. However, in the case of (unions of) acyclic conjunctive queries ((U)ACQs) there are some fundamental questions which are still open. It is the precise aim of ..."
Abstract
- Add to MetaCart
(Show Context)
The complete picture of the complexity of conjunctive query answer-ing under guarded disjunctive existential rules has been recently settled. However, in the case of (unions of) acyclic conjunctive queries ((U)ACQs) there are some fundamental questions which are still open. It is the precise aim of the present paper to close those questions, and to understand whether the acyclicity of the query has a positive impact on the complexity of query answering. Our main re-sult states that acyclic conjunctive query answering under a fixed set of guarded disjunctive existential rules is EXPTIME-hard. This result together with an EXP-TIME upper bound obtained by exploiting classical results on guarded first-order logic, gives us a complete picture of the complexity of our problem. We also show that our results can be used as a generic tool for establishing results on (U)ACQ answering under several central DLs. In fact, restricting the query lan-guage to UACQs improves the complexity to EXPTIME-complete for any DL between DL-Litebool and ALCHI; this holds even for fixed TBoxes.
Towards Efficient Reasoning Under Guarded-based Disjunctive Existential Rules
, 2014
"... The complete picture of the complexity of answering (unions of) conjunctive queries under the main guarded-based classes of disjunc-tive existential rules has been recently settled. It has been shown that the problem is very hard, namely 2ExpTime-complete, even for fixed sets of rules expressed in ..."
Abstract
- Add to MetaCart
The complete picture of the complexity of answering (unions of) conjunctive queries under the main guarded-based classes of disjunc-tive existential rules has been recently settled. It has been shown that the problem is very hard, namely 2ExpTime-complete, even for fixed sets of rules expressed in lightweight formalisms. This gives rise to the question whether its complexity can be reduced by restricting the query language. Several subclasses of conjunctive queries have been proposed with the aim of reducing the complexity of classical database problems such as query evaluation and query containment. Three of the most prominent subclasses of this kind are queries of bounded hypertree-width, queries of bounded treewidth and acyclic queries. The central objective of the present paper is to understand whether the above query languages have a positive impact on the complexity of query answering under the main guarded-based classes of disjunctive existential rules. We show that (unions of) conjunctive queries of bounded hypertree-width and of bounded treewidth do not reduce the complexity of our problem, even if we focus on predicates of bounded arity, or on fixed sets of disjunctive existential rules. Regarding acyclic queries, although our problem remains 2ExpTime-complete in general, in some relevant set-tings the complexity reduces to ExpTime-complete; in fact, this requires to bound the arity of the predicates, and for some expressive guarded-based formalisms, to fix the set of rules.
