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Wellfounded semantics for description logic programs in the Semantic Web
, 2009
"... The realization of the Semantic Web vision, in which computational logic has a prominent role, has stimulated a lot of research on combining rules and ontologies, which are formulated in different formalisms, into a framework that is more useful for describing semantic content. In particular, combin ..."
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Cited by 71 (19 self)
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The realization of the Semantic Web vision, in which computational logic has a prominent role, has stimulated a lot of research on combining rules and ontologies, which are formulated in different formalisms, into a framework that is more useful for describing semantic content. In particular, combining logic programming with the Web Ontology Language (OWL), which is a standard based on description logics, emerged as an important issue for linking the Rules and Ontology Layers of the Semantic Web. Nonmonotonic description logic programs (or dlprograms) were introduced for such a combination, in which a pair (L,P) of a description logic knowledge base L and a set of rules P with negation as failure is given a modelbased semantics that generalizes the answer set semantics of logic programs. In this paper, we reconsider dlprograms and present a wellfounded semantics for them as an analog for the other main semantics of logic programs. It generalizes the canonical definition of the wellfounded semantics based on unfounded sets, and, as we show, lifts many of the wellknown properties from ordinary logic programs to dlprograms. Among these properties: our semantics amounts to a partial model approximating the answer set semantics, which yields for positive and stratified dlprograms a total model coinciding with the answer set semantics; it has polynomial data complexity provided the access to the description logic
Russo,“Using event calculus to formalise policy specification and analysis,”
 in Policies for Distributed Systems and Networks, 2003. Proceedings. POLICY 2003. IEEE 4th International Workshop on. IEEE,
, 2003
"... Abstract As the interest in using policybased ..."
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ELP: Tractable rules for OWL 2
, 2008
"... 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 extendsEL ++ with a number ..."
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Cited by 66 (25 self)
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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 extendsEL ++ 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 DLsafe rules into ELP. While reasoning with DLsafe rules as such is already highly intractable, we show that DLsafe rules based on the Description Logic Programming (DLP) fragment of OWL 2 can be admitted in ELP without losing tractability.
SecPAL: Design and Semantics of a Decentralized Authorization Language
 In Proceedings of the 20th IEEE Computer Security Foundations Symposium (CSF
, 2006
"... By using or providing feedback on the SecPAL Specification (comprised of the SecPAL formal model, SecPAL Schema Specification, and SecPAL Schema) (“Specification”), you agree to the following terms and conditions: • Microsoft hereby grants you permission to copy and review the Specification (a) as a ..."
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Cited by 65 (5 self)
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By using or providing feedback on the SecPAL Specification (comprised of the SecPAL formal model, SecPAL Schema Specification, and SecPAL Schema) (“Specification”), you agree to the following terms and conditions: • Microsoft hereby grants you permission to copy and review the Specification (a) as a reference to assist you in planning and designing your implementation of the Specification and (b) to provide feedback on the Specification to Microsoft. You may not modify, create derivative works from, subset, or extend the Specification. • Provided that you comply with all the terms of use for the Specification, Microsoft agrees to grant you a royaltyfree license under reasonable and nondiscriminatory terms and conditions to Microsoft patents that Microsoft deems necessary to implement the Specification. You must comply with and implement all normative portions of the Specification in its entirety; you may not elect to implement only portions of the Specification. Unless otherwise specifically mentioned all sections of the Specification should be considered normative. • You have no obligation to give Microsoft any suggestions, comments or other feedback (“Feedback”) relating to the Specification. If you do give Microsoft Feedback on the Specification, You agree: (a) Microsoft may freely use, reproduce, license, distribute, and otherwise commercialize Your Feedback in any Microsoft product or service offering; (b) you also grant third parties, without charge, only those patent rights necessary to implement those portions of the Specification that incorporate your Feedback; and (c) you will not give Microsoft any Feedback (i) that you have reason to believe is subject to any patent, copyright or other intellectual property claim or right of any third party; or (ii) subject to license terms which seek to require any Microsoft product offering incorporating or derived from such Feedback, or other Microsoft intellectual property, to be licensed to or otherwise shared with any third party.
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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Cited by 62 (9 self)
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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
Probabilistic Logic Programming
 In Proc. of the 13th European Conf. on Artificial Intelligence (ECAI98
, 1998
"... . We present a new approach to probabilistic logic programs with a possible worlds semantics. Classical program clauses are extended by a subinterval of [0; 1] that describes the range for the conditional probability of the head of a clause given its body. We show that deduction in the defined proba ..."
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Cited by 62 (11 self)
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. We present a new approach to probabilistic logic programs with a possible worlds semantics. Classical program clauses are extended by a subinterval of [0; 1] that describes the range for the conditional probability of the head of a clause given its body. We show that deduction in the defined probabilistic logic programs is computationally more complex than deduction in classical logic programs. More precisely, restricted deduction problems that are Pcomplete for classical logic programs are already NPhard for probabilistic logic programs. We then elaborate a linear programming approach to probabilistic deduction that is efficient in interesting special cases. In the best case, the generated linear programs have a number of variables that is linear in the number of ground instances of purely probabilistic clauses in a probabilistic logic program. 1 INTRODUCTION There is already a quite extensive literature on probabilistic propositional logics and their various dialects. The most fa...
Answer Sets for Consistent Query Answering in Inconsistent Databases
 THEORY AND PRACTICE OF LOGIC PROGRAMMING
, 2003
"... A relational database is inconsistent if it does not satisfy a given set of integrity constraints. Nevertheless, it is likely that most of the data in it is consistent with the constraints. In this paper we apply logic programming based on answer sets to the problem of retrieving consistent informat ..."
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Cited by 53 (7 self)
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A relational database is inconsistent if it does not satisfy a given set of integrity constraints. Nevertheless, it is likely that most of the data in it is consistent with the constraints. In this paper we apply logic programming based on answer sets to the problem of retrieving consistent information from a possibly inconsistent database. Since consistent information persists from the original database to every of its minimal repairs, the approach is based on a specification of database repairs using disjunctive logic programs with exceptions, whose answer set semantics can be represented and computed by systems that implement stable model semantics. These programs allow us to declare persistence by default of data from the original instance to the repairs; and changes to restore consistency, by exceptions. We concentrate mainly on logic programs for binary integrity constraints, among which we find most of the integrity constraints found in practice.
The Lixto Data Extraction Project  Back and Forth between Theory and Practice
 PODS 2004
, 2004
"... We present the Lixto project, which is both a research project in database theory and a commercial enterprise that develops Web data extraction (wrapping) and Web service definition software. We discuss the project's main motivations and ideas, in particular the use of a logicbased framework ..."
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Cited by 52 (3 self)
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We present the Lixto project, which is both a research project in database theory and a commercial enterprise that develops Web data extraction (wrapping) and Web service definition software. We discuss the project's main motivations and ideas, in particular the use of a logicbased framework for wrapping. Then we present theoretical results on monadic datalog over trees and on Elog, its close relative which is used as the internal wrapper language in the Lixto system. These results include both a characterization of the expressive power and the complexity of these languages. We describe the visual wrapper specification process in Lixto and various practical aspects of wrapping. We discuss work on the complexity of query languages for trees that was inseminated by our theoretical study of logicbased languages for wrapping. Then we return to the practice of wrapping and the Lixto Transformation Server, which allows for streaming integration of data extracted from Web pages. This is a natural requirement in complex services based on Web wrapping. Finally, we discuss industrial applications of Lixto and point to open problems for future study.
On the Complexity of Nonrecursive XQuery and Functional Query Languages on Complex Values
 In Proc. PODS’05
"... This article studies the complexity of evaluating functional query languages for complex values such as monad algebra and the recursionfree fragment of XQuery. We show that monad algebra with equality restricted to atomic values is complete for the class TA[2O(n) , O(n)] of problems solvable in lin ..."
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Cited by 47 (2 self)
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This article studies the complexity of evaluating functional query languages for complex values such as monad algebra and the recursionfree fragment of XQuery. We show that monad algebra with equality restricted to atomic values is complete for the class TA[2O(n) , O(n)] of problems solvable in linear exponential time with a linear number of alternations. The monotone fragment of monad algebra with atomic value equality but without negation is complete for nondeterministic exponential time. For monad algebra with deep equality, we establish TA[2O(n) , O(n)] lower and exponentialspace upper bounds. We also study a fragment of XQuery, Core XQuery, that seems to incorporate all the features of a query language on complex values that are traditionally deemed essential. A close connection between monad algebra on lists and Core XQuery (with “child ” as the only axis) is exhibited, and it is shown that these languages are expressively equivalent up to representation issues. We show that Core XQuery is just as hard as monad algebra w.r.t. query and combined complexity, and that it is in TC0 if the query is assumed fixed. As Core XQuery is NEXPTIMEhard, it is commonly believed that any algorithm for evaluating Core XQuery has to require exponential amounts of working memory and doubly exponential time in the worst case. We present a property of queries – the lack of a certain form of composition – that virtually all realworld XQueries have and that allows for query evaluation in singly exponential time and polynomial space. Still, we are able to show for an important special case – Core XQuery with equality testing restricted to atomic values – that the compositionfree language is just as expressive as the language with composition. Thus, under widelyheld complexitytheoretic assumptions, the compositionfree language is an exponentially less succinct version of the language with composition.
Description Logic Rules
, 2008
"... We introduce description logic (DL) rules as a new rulebased 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 expressiv ..."
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Cited by 47 (21 self)
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We introduce description logic (DL) rules as a new rulebased 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 DLSROIQ – the basis for the ongoing standardisation of OWL 2 – can completely internalise DL rules. On the other hand, DL rules capture many expressive features ofSROIQ that are not available in simpler DLs yet. While reasoning inSROIQ is highly intractable, it turns out that DL rules can be introduced to various lightweight DLs without increasing their worstcase complexity. In particular, DL rules enable us to significantly extend the tractable DLsEL ++ and DLP.