Optimizing And Implementing Repair Programs For Consistent Query Answering In Databases
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Database Repairing and Consistent Query Answering
Integrity constraints are semantic conditions that a database should satisfy in order to be an appropriate model of external reality. In practice, and for many reasons, a database may not satisfy those integrity constraints, and for that reason it is said to be inconsistent. However, and most likely, a large portion of the database is still semantically correct, in a sense that has to be made precise. After having provided a formal characterization of consistent data in an inconsistent database, the natural problem emerges of extracting that semantically correct data, as query answers. The consistent data in an inconsistent database is usually characterized as the data that persists across all the database instances that are consistent and minimally differ from the inconsistent instance. Those are the so-called repairs of the database. In particular, the consistent answers to a query posed to the inconsistent database are those answers that can be simultaneously obtained from all the database repairs. As expected, the notion of repair requires an adequate notion of distance that allows for the comparison of databases with respect to how much they differ from the inconsistent instance. On this basis, the minimality condition on repairs can be properly formulated. In this monograph we present and discuss these fundamental concepts, different repair semantics, algorithms for computing consistent answers to queries, and also complexity-theoretic results related to the computation of repairs and doing consistent query answering. Table of Contents: Introduction / The Notions of Repair and Consistent Answer / Tractable CQA and Query Rewriting / Logically Specifying Repairs / Decision Problems in CQA: Complexity and Algorithms / Repairs and Data Cleaning
Scalable Uncertainty Management
This book constitutes the refereed proceedings of the First International Conference on Scalable Uncertainty Management, SUM 2007, held in Washington, DC, USA, in October 2007. The 20 revised full papers presented were carefully reviewed and selected from numerous submissions for inclusion in the book. The papers address artificial intelligence researchers, database researchers and practitioners.
Optimizing Repair Programs for Consistent Query Answering in Databases
Author: Monica Caniupan
language: en
Publisher: LAP Lambert Academic Publishing
Release Date: 2011-05
Databases may not always satisfy their integrity constraints (ICs). 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 answers obtained from every minimally repaired and consistent version of the database. Database repairs can be specied as stable models of disjunctive logic programs. Consistent Query Answering (CQA) for first-order queries is translated into cautious reasoning under the stable models semantics. Using logic programs in a straightforward manner is usually inefficient. We develop optimized techniques to evaluate queries over inconsistent databases by using logic programs. We optimize the structure of programs, model computation, and evaluation of queries from them. Moreover, we propose the use of the well-founded semantics (WFS) as an alternative way to obtain consistent answers. The WFS has lower data complexity than the stable models semantics. We also extend the use of logic programs for retrieving consistent answers to aggregate queries, and we develop a repair semantics for Data Warehouses.