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41
Logic Programming and Knowledge Representation  the AProlog perspective
 Artificial Intelligence
, 2002
"... In this paper we give a short introduction to logic programming approach to knowledge representation and reasoning. The intention is to help the reader to develop a 'feel' for the field's history and some of its recent developments. The discussion is mainly limited to logic programs under the answer ..."
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Cited by 87 (0 self)
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In this paper we give a short introduction to logic programming approach to knowledge representation and reasoning. The intention is to help the reader to develop a 'feel' for the field's history and some of its recent developments. The discussion is mainly limited to logic programs under the answer set semantics. For understanding of approaches to logic programming build on wellfounded semantics, general theories of argumentation, abductive reasoning, etc., the reader is referred to other publications.
A CostBased Model and Effective Heuristic for Repairing Constraints by Value Modification
 In ACM SIGMOD International Conference on Management of Data
, 2005
"... Data integrated from multiple sources may contain inconsistencies that violate integrity constraints. The constraint repair problem attempts to find “low cost ” changes that, when applied, will cause the constraints to be satisfied. While in most previous work repair cost is stated in terms of tuple ..."
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Cited by 64 (10 self)
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Data integrated from multiple sources may contain inconsistencies that violate integrity constraints. The constraint repair problem attempts to find “low cost ” changes that, when applied, will cause the constraints to be satisfied. While in most previous work repair cost is stated in terms of tuple insertions and deletions, we follow recent work to define a database repair as a set of value modifications. In this context, we introduce a novel cost framework that allows for the application of techniques from recordlinkage to the search for good repairs. We prove that finding minimalcost repairs in this model is NPcomplete in the size of the database, and introduce an approach to heuristic repairconstruction based on equivalence classes of attribute values. Following this approach, we define two greedy algorithms. While these simple algorithms take time cubic in the size of the database, we develop optimizations inspired by algorithms for duplicaterecord detection that greatly improve scalability. We evaluate our framework and algorithms on synthetic and real data, and show that our proposed optimizations greatly improve performance at little or no cost in repair quality. 1.
Conditional functional dependencies for data cleaning
 In ICDE
, 2007
"... We propose a class of constraints, referred to as conditional functional dependencies (CFDs), and study their applications in data cleaning. In contrast to traditional functional dependencies (FDs) that were developed mainly for schema design, CFDs aim at capturing the consistency of data by incorpo ..."
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Cited by 41 (5 self)
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We propose a class of constraints, referred to as conditional functional dependencies (CFDs), and study their applications in data cleaning. In contrast to traditional functional dependencies (FDs) that were developed mainly for schema design, CFDs aim at capturing the consistency of data by incorporating bindings of semantically related values. For CFDs we provide an inference system analogous to Armstrong’s axioms for FDs, as well as consistency analysis. Since CFDs allow data bindings, a large number of individual constraints may hold on a table, complicating detection of constraint violations. We develop techniques for detecting CFD violations in SQL as well as novel techniques for checking multiple constraints in a single query. We experimentally evaluate the performance of our CFDbased methods for inconsistency detection. This not only yields a constraint theory for CFDs butisalsoasteptowardapractical constraintbased method for improving data quality. 1
Conditional functional dependencies for capturing data inconsistencies
 TODS
"... We propose a class of integrity constraints for relational databases, referred to as conditional functional dependencies (cfds), and study their applications in data cleaning. In contrast to traditional functional dependencies (fds) that were developed mainly for schema design, cfds aim at capturing ..."
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Cited by 32 (6 self)
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We propose a class of integrity constraints for relational databases, referred to as conditional functional dependencies (cfds), and study their applications in data cleaning. In contrast to traditional functional dependencies (fds) that were developed mainly for schema design, cfds aim at capturing the consistency of data by enforcing bindings of semantically related values. For static analysis of cfds we investigate the consistency problem, which is to determine whether or not there exists a nonempty database satisfying a given set of cfds, and the implication problem, which is to decide whether or not a set of cfds entails another cfd. We show that while any set of transitional fds is trivially consistent, the consistency problem is npcomplete for cfds, but it is in ptime when either the database schema is predefined or no attributes involved in the cfds have a finite domain. For the implication analysis of cfds, we provide an inference system analogous to Armstrong’s axioms for fds, and show that the implication problem is conpcomplete for cfds in contrast to the lineartime complexity for their traditional counterpart. We also present an algorithm for computing a minimal cover of a set of cfds. Since cfds allow data bindings, in some cases cfds may be physically large, complicating detection of constraint violations. We develop techniques for detecting cfd violations in sql as well as novel techniques for checking multiple
Complexity and Approximation of Fixing Numerical Attributes in Databases Under Integrity Constraints
 In International Workshop on Database Programming Languages
, 2005
"... Abstract. Consistent query answering is the problem of computing the answers from a database that are consistent with respect to certain integrity constraints that the database as a whole may fail to satisfy. Those answers are characterized as those that are invariant under minimal forms of restorin ..."
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Cited by 30 (12 self)
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Abstract. Consistent query answering is the problem of computing the answers from a database that are consistent with respect to certain integrity constraints that the database as a whole may fail to satisfy. Those answers are characterized as those that are invariant under minimal forms of restoring the consistency of the database. In this context, we study the problem of repairing databases by fixing integer numerical values at the attribute level with respect to denial and aggregate constraints. We introduce a quantitative definition of database fix, and investigate the complexity of several problems such as DFP, i.e. the existence of fixes within a given distance from the original instance, and CQA, i.e. deciding consistency of answers to aggregate conjunctive queries under different semantics. We provide sharp complexity bounds, identify relevant tractable cases; and introduce approximation algorithms for some of those that are intractable. More specifically, we obtain results like undecidability of existence of fixes for aggregate constraints; MAXSNPhardness of DFP, but a good approximation algorithm for a relevant special case; and intractability but good approximation for CQA for aggregate queries for one database atom denials (plus builtins). 1
Complexity of Consistent Query Answering in Databases under CardinalityBased and Incremental Repair Semantics
 In ICDT
, 2007
"... Abstract. Consistent Query Answering (CQA) is the problem of computing from a database the answers to a query that are consistent with respect to certain integrity constraints that the database, as a whole, may fail to satisfy. Consistent answers have been characterized as those that are invariant u ..."
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Cited by 30 (9 self)
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Abstract. Consistent Query Answering (CQA) is the problem of computing from a database the answers to a query that are consistent with respect to certain integrity constraints that the database, as a whole, may fail to satisfy. Consistent answers have been characterized as those that are invariant under certain minimal forms of restoration of the database consistency. In this paper we investigate algorithmic and complexity theoretic issues of CQA under database repairs that minimally departwrt the cardinality of the symmetric difference from the original database. Research on this kind of repairs has been suggested in the literature, but no systematic study had been done. Here we obtain first tight complexity bounds. We also address, considering for the first time a dynamic scenario for CQA, the problem of incremental complexity of CQA, that naturally occurs when an originally consistent database becomes inconsistent after the execution of a sequence of update operations. Tight bounds on incremental complexity are provided for various semantics under denial constraints, e.g. (a) minimum tuplebased repairs wrt cardinality, (b) minimal tuplebased repairs wrt set inclusion, and (c) minimum numerical aggregation of attributebased repairs. Fixed parameter tractability is also investigated in this dynamic context, where the size of the update sequence becomes the relevant parameter. 1
Extending Dependencies with Conditions
"... This paper introduces a class of conditional inclusion dependencies (CINDs), which extends traditional inclusion dependencies (INDs) by enforcing bindings of semantically related data values. We show that CINDs are useful not only in data cleaning, but are also in contextual schema matching [7]. To ..."
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Cited by 26 (7 self)
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This paper introduces a class of conditional inclusion dependencies (CINDs), which extends traditional inclusion dependencies (INDs) by enforcing bindings of semantically related data values. We show that CINDs are useful not only in data cleaning, but are also in contextual schema matching [7]. To make effective use of CINDs in practice, it is often necessary to reason about them. The most important static analysis issue concerns consistency, to determine whether or not a given set of CINDs has conflicts. Another issue concerns implication, i.e., deciding whether a set of CINDs entails another CIND. We give a full treatment of the static analyses of CINDs, and show that CINDs retain most nice properties of traditional INDs: (a) CINDs are always consistent; (b) CINDs are finitely axiomatizable, i.e., there exists a sound and complete inference system for implication of CINDs; and (c) the implication problem for CINDs has the same complexity as its traditional counterpart, namely, PSPACEcomplete, in the absence of attributes with a finite domain; but it is EXPTIMEcomplete in the general setting. In addition, we investigate the interaction between CINDs and conditional functional dependencies (CFDs), an extension of functional dependencies proposed in [9]. We show that the consistency problem for the combination of CINDs and CFDs becomes undecidable. In light of the undecidability, we provide heuristic algorithms for the consistency analysis of CFDs and CINDs, and experimentally verify the effectiveness and efficiency of our algorithms. 1.
Repair Checking in Inconsistent Databases: Algorithms and Complexity
 Proc. of the International Conference on Database Theory (ICDT
"... Managing inconsistency in databases has long been recognized as an important problem. One of the most promising approaches to coping with inconsistency in databases is the framework of database repairs, which has been the topic of an extensive investigation over the past several years. Intuitively, ..."
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Cited by 26 (1 self)
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Managing inconsistency in databases has long been recognized as an important problem. One of the most promising approaches to coping with inconsistency in databases is the framework of database repairs, which has been the topic of an extensive investigation over the past several years. Intuitively, a repair of an inconsistent database is a consistent database that differs from the given inconsistent database in a minimal way. So far, most of the work in this area has addressed the problem of obtaining the consistent answers to a query posed on an inconsistent database. Repair checking is the following decision problem: given two databases r and r ′ , is r ′ a repair of r? Although repair checking is a fundamental algorithmic problem about inconsistent databases, it has not received as much attention as consistent query answering. In this paper, we give a polynomialtime algorithm for subsetrepair checking under integrity constraints that are the union of a weakly acyclic set of localasview (LAV) tuplegenerating dependencies and a set of equalitygenerating dependencies. This result significantly generalizes earlier work for subsetrepair checking when the integrity constraints are the union of an acyclic set of inclusion dependencies and a set of functional dependencies. We also give a polynomialtime algorithm for symmetricdifference repair checking, when the integrity constraints form a weakly acyclic set of LAV tgds. After this, we establish a number of complexitytheoretic results that delineate the boundary between tractability and intractability for the repairchecking problem. Specifically, we show that the aforementioned tractability
Increasing the expressivity of conditional functional dependencies without extra complexity
 In Proceedings of the International Conference on Data Engineering
"... Abstract — The paper proposes an extension of CFDs [1], referred to as extended Conditional Functional Dependencies (eCFDs). In contrast to CFDs, eCFDs specify patterns of semantically related values in terms of disjunction and inequality, and are capable of catching inconsistencies that arise in pr ..."
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Cited by 16 (4 self)
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Abstract — The paper proposes an extension of CFDs [1], referred to as extended Conditional Functional Dependencies (eCFDs). In contrast to CFDs, eCFDs specify patterns of semantically related values in terms of disjunction and inequality, and are capable of catching inconsistencies that arise in practice but cannot be detected by CFDs. The increase in expressive power does not incur extra complexity: we show that the satisfiability and implication analyses of eCFDs remain NPcomplete and coNPcomplete, respectively, the same as their CFDs counterparts. In light of the intractability, we present an algorithm that approximates the maximum number of eCFDs that are satisfiable. In addition, we revise SQL techniques for detecting CFD violations, and show that violations of multiple eCFDs can be captured via a single pair of SQL queries. We also introduce an incremental SQL technique for detecting eCFD violations in response to database updates. We experimentally verify the effectiveness and efficiency of our SQLbased detection methods. I.
The Consistency Extractor System: Answer Set Programs for Consistent Query Answering in Databases
, 2010
"... We describe the Consistency Extractor System (ConsEx) that computes consistent answers to Datalog queries with negation posed to relational databases that may be inconsistent with respect to certain integrity constraints. In order to solve this task, ConsEx uses answers set programming. More precise ..."
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Cited by 12 (8 self)
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We describe the Consistency Extractor System (ConsEx) that computes consistent answers to Datalog queries with negation posed to relational databases that may be inconsistent with respect to certain integrity constraints. In order to solve this task, ConsEx uses answers set programming. More precisely, ConsEx uses disjunctive logic programs with stable models semantics to specify and reason with the repairs, i.e. with the consistent virtual instances that minimally depart from the original database. The consistent information is invariant under all repairs. ConsEx achieves efficient query evaluation by implementing magic sets techniques. We describe the general methodology, its optimizations for query answering, and the architecture of the system. We also present encouraging experimental results.