Results 11  20
of
37
Characterizing and Computing Semantically Correct Answers from Databases with Annotated Logic and Answer Sets
"... A relational database may not satisfy certain integrity constraints (ICs) for several reasons. However most likely most of the information in it is still consistent with the ICs. The answers to queries that are consistent with the ICs can be considered sematically correct answers, and are characteri ..."
Abstract

Cited by 32 (21 self)
 Add to MetaCart
A relational database may not satisfy certain integrity constraints (ICs) for several reasons. However most likely most of the information in it is still consistent with the ICs. The answers to queries that are consistent with the ICs can be considered sematically correct answers, and are characterized [2] as ordinary answers that can be obtained from every minimally repaired version of the database. In this paper we address the problem of specifying those repaired versions as the minimal models of a theory written in Annotated Predicate Logic [27]. It is also shown how to specify database repairs using disjunctive logic program with annotation arguments and a classical stable model semantics.
Social contraction and belief negotiation
 In Proceedings of KR’02
, 2002
"... An intelligent agent may receive information about its environment from several different sources. How should the agent merge these items of information into a single, consistent piece? Taking our lead from the contraction + expansion approach to belief revision, we envisage a twostage approach to ..."
Abstract

Cited by 28 (1 self)
 Add to MetaCart
An intelligent agent may receive information about its environment from several different sources. How should the agent merge these items of information into a single, consistent piece? Taking our lead from the contraction + expansion approach to belief revision, we envisage a twostage approach to this problem. The first stage consists of weakening the individual pieces of information into a form in which they can be consistently added together. The second, trivial, stage then consists of simply adding together the information thus obtained. This paper is devoted mainly to the first stage of this process, which we call social contraction. We consider both a postulational and a procedural approach to social contraction. The latter builds on the authorÕs framework of belief negotiation models. With the help of Spohntype rankings we provide two possible instantiations of this extended framework. This leads to two interesting concrete families of social contraction functions. Ó 2005 Elsevier B.V. All rights reserved.
Scalar Aggregation in Inconsistent Databases
, 2003
"... We consider herescalq aggregation queries in databases that mayviolzz a given set of functional dependencies. We de#ne consistent answers to such queries to begreatestlEzqglzqgl upper bounds on thevalq of thescalW function acrossal (minimal repairs of the database. We show how to compute such answe ..."
Abstract

Cited by 28 (5 self)
 Add to MetaCart
We consider herescalq aggregation queries in databases that mayviolzz a given set of functional dependencies. We de#ne consistent answers to such queries to begreatestlEzqglzqgl upper bounds on thevalq of thescalW function acrossal (minimal repairs of the database. We show how to compute such answers. We provide acomplWg characterization of thecomputational compltati of thisproblz Wealf show howtractabilfx can be improved inseveral special cases (oneinvolfz anovel applNgjfzz of BoyceCoddNormal Form) and present apractical hybrid queryevalq###x method.
Magic Sets and their Application to Data Integration
 In Proc. International Conference on Database Theory (ICDT 05), Springer LNCS 3363, 2005
, 2005
"... Abstract. We propose a generalization of the wellknown Magic Sets technique to Datalog ¬ programs with (possibly unstratified) negation under stable model semantics. Our technique produces a new program whose evaluation is generally more efficient (due to a smaller instantiation), while preserving ..."
Abstract

Cited by 25 (4 self)
 Add to MetaCart
Abstract. We propose a generalization of the wellknown Magic Sets technique to Datalog ¬ programs with (possibly unstratified) negation under stable model semantics. Our technique produces a new program whose evaluation is generally more efficient (due to a smaller instantiation), while preserving soundness under cautious reasoning. Importantly, if the original program is consistent, then full queryequivalence is guaranteed for both brave and cautious reasoning, which turn out to be sound and complete. In order to formally prove the correctness of our Magic Sets transformation, we introduce a novel notion of modularity for Datalog ¬ under the stable model semantics, which is relevant per se. We prove that a module can be evaluated independently from the rest of the program, while preserving soundness under cautious reasoning. For consistent programs, both soundness and completeness are guaranteed for brave reasoning and cautious reasoning as well. Our Magic Sets optimization constitutes an effective method for enhancing the performance of dataintegration systems in which queryanswering is carried out by means of cautious reasoning over Datalog ¬ programs. In fact, preliminary results of experiments in the EU project INFOMIX, show that Magic Sets are fundamental for the scalability of the system. 1
On the Computational Complexity of MinimalChange Integrity Maintenance in Relational Databases
 IN BERTOSSI ET AL
, 2004
"... We address the problem of minimalchange integrity maintenance in the context of integrity constraints in relational databases. Using the framework proposed by Arenas, Bertossi, and Chomicki [4], we focus on two basic computational issues: repair checking (is a database instance a repair of a given ..."
Abstract

Cited by 19 (3 self)
 Add to MetaCart
We address the problem of minimalchange integrity maintenance in the context of integrity constraints in relational databases. Using the framework proposed by Arenas, Bertossi, and Chomicki [4], we focus on two basic computational issues: repair checking (is a database instance a repair of a given database?) and consistent query answers (is a tuple an answer to a given query in every repair of a given database?). We study the computational complexity of both problems, delineating the boundary between the tractable and the intractable. We review relevant semantical issues and survey different computational mechanisms proposed in this context. Our analysis sheds light on the computational feasibility of minimalchange integrity maintenance. The tractable cases should lead to practical implementations. The intractability results highlight the inherent limitations of any integrity enforcement mechanism, e.g., triggers or referential constraint actions, as a way of performing minimalchange integrity maintenance.
Disjunctive Deductive Databases for Computing Certain and Consistent Answers to Queries from Mediated Data Integration Systems
 Journal of Applied Logic
"... We address the problem of retrieving certain and consistent answers to queries posed to a mediated data integration system with open sources under the localasview paradigm using conjunctive and disjunctive view definitions. For obtaining certain answers a query program is run on top of a norma ..."
Abstract

Cited by 15 (3 self)
 Add to MetaCart
We address the problem of retrieving certain and consistent answers to queries posed to a mediated data integration system with open sources under the localasview paradigm using conjunctive and disjunctive view definitions. For obtaining certain answers a query program is run on top of a normal deductive database with choice that defines the class of minimal legal instances of the integration system under the cautious stable model semantics. This methodology works for all monotone Datalog queries. To compute answers to queries that are consistent wrt given global integrity constraints, the specification of minimal legal instances is combined with another disjunctive deductive database that specifies the repairs of those legal instances. This allows to retrieve the consistent answers to any Datalog query, for any set of universal and acyclic referential integrity constraints.
Towards automated integration of guess and check programs in answer set programming: a metainterpreter and applications. Theory and Practice of Logic Programming 6
"... Abstract. Answer set programming (ASP) with disjunction offers a powerful tool for declaratively representing and solving hard problems. Many NPcomplete problems can be encoded in the answer set semantics of logic programs in a very concise and intuitive way, where the encoding reflects the typical ..."
Abstract

Cited by 14 (3 self)
 Add to MetaCart
Abstract. Answer set programming (ASP) with disjunction offers a powerful tool for declaratively representing and solving hard problems. Many NPcomplete problems can be encoded in the answer set semantics of logic programs in a very concise and intuitive way, where the encoding reflects the typical “guess and check ” nature of NP problems: The property is encoded in a way such that polynomial size certificates for it correspond to stable models of a program. However, the problemsolving capacity of full disjunctive logic programs (DLPs) is beyond NP, and captures a class of problems at the second level of the polynomial hierarchy. While these problems also have a clear “guess and check ” structure, finding an encoding in a DLP reflecting this structure may sometimes be a nonobvious task, in particular if the “check ” itself is a coNPcomplete problem; usually, such problems are solved by interleaving separate guess and check programs, where the check is expressed by inconsistency of the check program. In this paper, we present general transformations of headcycle free (extended) disjunctive logic programs into stratified and positive (extended) disjunctive logic programs based on metainterpretation techniques. The answer sets of the original and the transformed program are in simple correspondence, and, moreover, inconsistency of the original program is indicated by a designated answer set of the transformed program. Our transformations facilitate the integration of separate “guess ” and “check”
Repairing Databases with Annotated Predicate Logic
 Ninth International Workshop on NonMonotonic Reasoning (NMR02), Special Session: Changing and Integrating Information: From Theory to Practice
, 2002
"... Consistent answers from a relational database that violates a given set of integrity constraints are characterized [Arenas et al. 1999] as ordinary answers that can be obtained from every repaired version of the database. In this paper we address the problem of specifying the repairs of a database a ..."
Abstract

Cited by 13 (7 self)
 Add to MetaCart
Consistent answers from a relational database that violates a given set of integrity constraints are characterized [Arenas et al. 1999] as ordinary answers that can be obtained from every repaired version of the database. In this paper we address the problem of specifying the repairs of a database as the minimal models of a theory written in Annotated Predicate Logic [Kifer et al. 1992a]. The specification is then transformed into a disjunctive logic program with annotation arguments and a stable model semantics. From the program, consistent answers to first order queries are obtained.
Database repair by signed formulae
 In Seipel, D., & TurellTorres, J. (Eds.), Proc. 3rd Int. Symp. on Foundations of Information and Knowledge Systems (FoIKS’04), No. 2942 in LNCS
, 2004
"... Abstract. We introduce a simple and practically efficient method for repairing inconsistent databases. The idea is to properly represent the underlying problem, and then use offtheshelf applications for efficiently computing the corresponding solutions. Given a possibly inconsistent database, we r ..."
Abstract

Cited by 12 (2 self)
 Add to MetaCart
Abstract. We introduce a simple and practically efficient method for repairing inconsistent databases. The idea is to properly represent the underlying problem, and then use offtheshelf applications for efficiently computing the corresponding solutions. Given a possibly inconsistent database, we represent the possible ways to restore its consistency in terms of signed formulae. Then we show how the ‘signed theory ’ that is obtained can be used by a variety of computational models for processing quantified Boolean formulae, or by constraint logic program solvers, in order to rapidly and efficiently compute desired solutions, i.e., consistent repairs of the database. 1