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Jan Chomicki

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5 papers

2 author rows

TIME Conference 2016 Conference Paper

Consistent Query Answering for Atemporal Constraints over Temporal Databases

Jan Chomicki
Jef Wijsen

Consistent query answering is a principled approach to query answering on inconsistent databases: when an inconsistent database has more than one plausible repair, queries are answered by returning the intersection of the query answers over all repairs. In this paper, we study consistent query answering over temporal databases relative to atemporal integrity constraints. A temporal database is conceptually viewed as a sequence of atemporal snapshot databases indexed by time. Two approaches to repairing are presented. In the first approach, each snapshot database is repaired individually and independently of earlier or later snapshots. This independence between snapshots facilitates the computation of consistent query answers. A second approach, which is seemingly more realistic, favors the persistence of attribute values in repairs.

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AIJ Journal 2011 Journal Article

Contracting preference relations for database applications

Denis Mindolin
Jan Chomicki

The binary relation framework has been shown to be applicable to many real-life preference handling scenarios. Here we study preference contraction: the problem of discarding selected preferences. We argue that the property of minimality and the preservation of strict partial orders are crucial for contractions. Contractions can be further constrained by specifying which preferences should be protected. We consider preference relations that are finite or finitely representable using preference formulas. We present algorithms for computing minimal and preference-protecting minimal contractions for finite as well as finitely representable preference relations. We study relationships between preference change in the binary relation framework and belief change in the belief revision theory. We evaluate the proposed algorithms experimentally and present the results.

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I&C Journal 2005 Journal Article

Minimal-change integrity maintenance using tuple deletions

Jan Chomicki
Jerzy Marcinkowski

We address the problem of minimal-change integrity maintenance in the context of integrity constraints in relational databases. We assume that integrity-restoration actions are limited to tuple deletions. We focus on two basic computational issues: repair checking (is a database instance a repair of a given database?) and consistent query answers [in: ACM Symposium on Principles of Database Systems (PODS), 1999, 68] (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 cases. We consider denial constraints, general functional and inclusion dependencies, as well as key and foreign key constraints. Our results shed light on the computational feasibility of minimal-change 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 minimal-change integrity maintenance.

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TCS Journal 2003 Journal Article

Scalar aggregation in inconsistent databases

Marcelo Arenas
Leopoldo Bertossi
Jan Chomicki
Xin He
Vijay Raghavan
Jeremy Spinrad

We consider here scalar aggregation queries in databases that may violate a given set of functional dependencies. We define consistent answers to such queries to be greatest-lowest/least-upper bounds on the value of the scalar function across all (minimal) repairs of the database. We show how to compute such answers. We provide a complete characterization of the computational complexity of this problem. We also show how tractability can be improved in several special cases (one involves a novel application of Boyce–Codd Normal Form) and present a practical hybrid query evaluation method.

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TIME Conference 1999 Conference Paper

A Geometric Framework for Specifying Spatiotemporal Objects

Jan Chomicki
Peter Z. Revesz

We present a framework for specifying spatiotemporal objects using spatial and temporal objects, and a geometric transformation. We define a number of classes of spatiotemporal objects and study their closure properties.

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