61 research outputs found
Answer Sets for Consistent Query Answering in Inconsistent Databases
A relational database is inconsistent if it does not satisfy a given set of
integrity constraints. Nevertheless, it is likely that most of the data in it
is consistent with the constraints. In this paper we apply logic programming
based on answer sets to the problem of retrieving consistent information from a
possibly inconsistent database. Since consistent information persists from the
original database to every of its minimal repairs, the approach is based on a
specification of database repairs using disjunctive logic programs with
exceptions, whose answer set semantics can be represented and computed by
systems that implement stable model semantics. These programs allow us to
declare persistence by defaults and repairing changes by exceptions. We
concentrate mainly on logic programs for binary integrity constraints, among
which we find most of the integrity constraints found in practice.Comment: 34 page
Paraconsistent logic and query answering in inconsistent databases
This paper concerns the paraconsistent logic LPQ and
an application of it in the area of relational database theory. The notions of
a relational database, a query applicable to a relational database, and a
consistent answer to a query with respect to a possibly inconsistent relational
database are considered from the perspective of this logic. This perspective
enables among other things the definition of a consistent answer to a query
with respect to a possibly inconsistent database without resort to database
repairs. In a previous paper, LPQ is presented with a
sequent-style natural deduction proof system. In this paper, a sequent calculus
proof system is presented because it is common to use a sequent calculus proof
system as the basis of proof search procedures and such procedures may form the
core of algorithms for computing consistent answers to queries.Comment: 21 pages; revision of v4, some inaccuracies removed and material
streamlined at several place
Matching Dependencies with Arbitrary Attribute Values: Semantics, Query Answering and Integrity Constraints
Matching dependencies (MDs) were introduced to specify the identification or
matching of certain attribute values in pairs of database tuples when some
similarity conditions are satisfied. Their enforcement can be seen as a natural
generalization of entity resolution. In what we call the "pure case" of MDs,
any value from the underlying data domain can be used for the value in common
that does the matching. We investigate the semantics and properties of data
cleaning through the enforcement of matching dependencies for the pure case. We
characterize the intended clean instances and also the "clean answers" to
queries as those that are invariant under the cleaning process. The complexity
of computing clean instances and clean answers to queries is investigated.
Tractable and intractable cases depending on the MDs and queries are
identified. Finally, we establish connections with database "repairs" under
integrity constraints.Comment: 13 pages, double column, 2 figure
Anytime Computation of Cautious Consequences in Answer Set Programming
Query answering in Answer Set Programming (ASP) is usually solved by
computing (a subset of) the cautious consequences of a logic program. This task
is computationally very hard, and there are programs for which computing
cautious consequences is not viable in reasonable time. However, current ASP
solvers produce the (whole) set of cautious consequences only at the end of
their computation. This paper reports on strategies for computing cautious
consequences, also introducing anytime algorithms able to produce sound answers
during the computation.Comment: To appear in Theory and Practice of Logic Programmin
A SAT-based System for Consistent Query Answering
An inconsistent database is a database that violates one or more integrity
constraints, such as functional dependencies. Consistent Query Answering is a
rigorous and principled approach to the semantics of queries posed against
inconsistent databases. The consistent answers to a query on an inconsistent
database is the intersection of the answers to the query on every repair, i.e.,
on every consistent database that differs from the given inconsistent one in a
minimal way. Computing the consistent answers of a fixed conjunctive query on a
given inconsistent database can be a coNP-hard problem, even though every fixed
conjunctive query is efficiently computable on a given consistent database.
We designed, implemented, and evaluated CAvSAT, a SAT-based system for
consistent query answering. CAvSAT leverages a set of natural reductions from
the complement of consistent query answering to SAT and to Weighted MaxSAT. The
system is capable of handling unions of conjunctive queries and arbitrary
denial constraints, which include functional dependencies as a special case. We
report results from experiments evaluating CAvSAT on both synthetic and
real-world databases. These results provide evidence that a SAT-based approach
can give rise to a comprehensive and scalable system for consistent query
answering.Comment: 25 pages including appendix, to appear in the 22nd International
Conference on Theory and Applications of Satisfiability Testin
Priority-Based Conflict Resolution in Inconsistent Relational Databases
We study here the impact of priorities on conflict resolution in inconsistent
relational databases. We extend the framework of repairs and consistent query
answers. We propose a set of postulates that an extended framework should
satisfy and consider two instantiations of the framework: (locally preferred)
l-repairs and (globally preferred) g-repairs. We study the relationships
between them and the impact each notion of repair has on the computational
complexity of repair checking and consistent query answers
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