5,034 research outputs found
Constrained Query Answering
Traditional answering methods evaluate queries only against positive
and definite knowledge expressed by means of facts and deduction rules. They do
not make use of negative, disjunctive or existential information. Negative or indefinite
knowledge is however often available in knowledge base systems, either as
design requirements, or as observed properties. Such knowledge can serve to rule out
unproductive subexpressions during query answering. In this article, we propose an
approach for constraining any conventional query answering procedure with general,
possibly negative or indefinite formulas, so as to discard impossible cases and to
avoid redundant evaluations. This approach does not impose additional conditions
on the positive and definite knowledge, nor does it assume any particular semantics
for negation. It adopts that of the conventional query answering procedure it
constrains. This is achieved by relying on meta-interpretation for specifying the
constraining process. The soundness, completeness, and termination of the underlying
query answering procedure are not compromised. Constrained query answering
can be applied for answering queries more efficiently as well as for generating more
informative, intensional answers
Open issues in semantic query optimization in relational DBMS
After two decades of research into Semantic Query Optimization (SQO) there is clear agreement as to the efficacy of SQO. However, although there are some experimental implementations there are still no commercial implementations. We
first present a thorough analysis of research into SQO. We identify three problems which inhibit the effective use of SQO in Relational Database Management Systems(RDBMS). We then propose solutions to these problems and describe first steps towards the implementation of an effective semantic query optimizer for relational databases
Structuring the process of integrity maintenance (extended version)
Two different approaches have been traditionally considered for dealing with the process of integrity constraints
enforcement: integrity checking and integrity maintenance. However, while previous research in the first approach has
mainly addressed efficiency issues, research in the second approach has been mainly concentrated in being able to
generate all possible repairs that falsify an integrity constraint violation. In this paper we address efficiency issues during
the process of integrity maintenance. In this sense, we propose a technique which improves efficiency of existing methods
by defining the order in which maintenance of integrity constraints should be performed. Moreover, we use also this
technique for being able to handle in an integrated way the integrity constraintsPostprint (published version
The DLV System for Knowledge Representation and Reasoning
This paper presents the DLV system, which is widely considered the
state-of-the-art implementation of disjunctive logic programming, and addresses
several aspects. As for problem solving, we provide a formal definition of its
kernel language, function-free disjunctive logic programs (also known as
disjunctive datalog), extended by weak constraints, which are a powerful tool
to express optimization problems. We then illustrate the usage of DLV as a tool
for knowledge representation and reasoning, describing a new declarative
programming methodology which allows one to encode complex problems (up to
-complete problems) in a declarative fashion. On the foundational
side, we provide a detailed analysis of the computational complexity of the
language of DLV, and by deriving new complexity results we chart a complete
picture of the complexity of this language and important fragments thereof.
Furthermore, we illustrate the general architecture of the DLV system which
has been influenced by these results. As for applications, we overview
application front-ends which have been developed on top of DLV to solve
specific knowledge representation tasks, and we briefly describe the main
international projects investigating the potential of the system for industrial
exploitation. Finally, we report about thorough experimentation and
benchmarking, which has been carried out to assess the efficiency of the
system. The experimental results confirm the solidity of DLV and highlight its
potential for emerging application areas like knowledge management and
information integration.Comment: 56 pages, 9 figures, 6 table
Automatic generation of simplified weakest preconditions for integrity constraint verification
Given a constraint assumed to hold on a database and an update to
be performed on , we address the following question: will still hold
after is performed? When is a relational database, we define a
confluent terminating rewriting system which, starting from and ,
automatically derives a simplified weakest precondition such that,
whenever satisfies , then the updated database will satisfy
, and moreover is simplified in the sense that its computation
depends only upon the instances of that may be modified by the update. We
then extend the definition of a simplified to the case of deductive
databases; we prove it using fixpoint induction
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