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.

Abstract. We present the Consistency Extractor System (ConsEx) that uses answer set programming to compute consistent answers to first-order queries posed to relational databases that may be inconsistent wrt their integrity constraints. Among other features, ConsEx implements a magic sets technique to evaluate queries via disjunctive logic programs with stable model semantics that specify the repair of the original database. We describe the methodology and the system; and also present some experimental results. 1

Databases may not always satisfy their integrity constraints (ICs) and a number of different reasons can be held accountable for this. However, in most cases an important part of the data is still consistent with the ICs, and can still be retrieved through queries posed to the database. Consistent query answers are characterized as ordinary answers obtained from every minimally repaired and consistent version of the database. Database repairs wrt a wide class of ICs can be specified as stable models of disjunctive logic programs. Thus, Consistent Query Answering (CQA) for first-order queries is translated into cautious reasoning under the stable models semantics. The use of logic programs does not exceed the intrinsic complexity of CQA. However, using them in a straightforward manner is usually inefficient. The goal of this thesis is to develop optimized techniques to evaluate queries over inconsistent

Abstract. We propose and investigate a semantics for peer data exchange systems (or peer data management systems) where different peers are pairwise related to each other by means of data exchange constraints and trust relationships. These two elements plus the data at the peers’ sites and the local integrity constraints for a peer are made compatible via the proposed semantics by determining a set of solution instances, which are the intended virtual instances for the peer. The semantically correct answers from a peer to a query, called its peer consistent answers, are defined as those answers that are invariant under all its different solution instances. We show that solution instances can be specified as the models of logic programs with a stable model semantics. 1

c ○ Copyright by Loreto Bravo, 2007 For several reasons a database may not satisfy certain integrity constraints (ICs), for example, when it is the result of integrating several independent data sources. However, most likely, information in it is still consistent with the ICs; and could be retrieved when queries are answered. Consistent answers with respect to a set of ICs have been characterized as answers that can be obtained from every possible minimal repair of the database. The goal of this research is to develop methods to retrieve consistent answers for a wide and practical class of constraints and queries from relational databases and from data integration systems. We will put special interest on databases with null values. We will give a semantics of satisfaction of constraints in the presence of null that generalizes the one used in commercial DBMS. Since there are interesting connections between the area of consistently querying virtual data integration systems and other areas, like querying incomplete databases, merging inconsistent theories, semantic reconciliation of data, schema mapping, data exchange, and query answering in peer data management systems, the results of this research could also be applied to them. In our research, we explore in more depth the connection with virtual data integration systems and peer data management systems. ii To my husband

Abstract. A Data Warehouse (DW) is a data repository that integrates data from multiple sources and organizes the data according to a set of data structures called dimensions. Each dimension provides a perspective upon which the data can be viewed. In order to support an efficient processing of queries, a dimension is usually required to satisfy different classes of integrity constraints. In this paper, we study the problem of repairing a dimension when it fails to satisfy a set of two classes of integrity constraints: strictness constraints andcovering constraints. We introduce the notion of minimal repair of a dimension in this context. A minimal repair is defined as a new dimension that is consistent with respect to the integrity constraints, which is obtained by applying a minimal amount of updatestotheoriginal dimension. Westudythecomplexityofcomputing minimal repairs. Finally, we show how to characterize and compute minimal repairs of a dimension using Datalog programs with stable model semantics. 1

Abstract. Consistent answers to a query from an inconsistent database are answers that can be simultaneously retrieved from every possible repair; and repairs are consistent instances that minimally differ from the original instance. Database repairs can be specified as the stable models of a disjunctive logic program. In this paper we show how to use the repair programs to transform the problem of consistent query answering into a problem of reasoning wrt a concrete theory written in second-order predicate logic. It also investigated how a first-order theory can be obtained instead, by applying second-order quantifier elimination techniques. 1

Systems (IQIS 2004 and IQIS 2005)........................................................................................... 50

We present a declarative framework for updating views over indefinite databases, that is, databases with null values. The framework follows the standard database approach, which allows for a unique null constant. As the main contributions of the paper, we introduce the concept of an indefinite deductive database as a formal representation of a view over an indefinite database, propose a semantics for indefinite deductive databases, and use it to solve the integrity constraints maintenance and view update problems. To address the last issue, we define several classes of database repairs, with the class of constrained repairs as one of them. Constrained repairs form a narrow class of repairs that avoid arbitrary commitments (are grounded in the deductive database specification and the view update request), aim to change the database “minimally ” (satisfy a certain minimality condition we introduced that is attuned to the case of indefinite databases) and, in general, address several problems of earlier solutions to the view update problem.

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