Using Automated Reasoning Techniques for Deductive Databasis

This report presents a proposal for a deduction component that supports the query mechanism of relational databases. The query-subquery (QSQ) paradigm is currently very popular in the database community since it focuses the deduction process on the relevant data. We show how to extend the QSQ paradigm from Horn clauses to arbitrary predicate logic formulae such that disjunctions in the consequent of an implication, negation in its logical meaning and arbitrary recursive predicates can be handled without restrictions. Various techniques to improve the search behaviour, such as lemma generation, query generalization etc. can be incorporated. Furthermore we show how to use clause graphs for compile time optimizations in the presence of recursive clauses and to support the run time processing

Web and Semantic Web Query Languages

A number of techniques have been developed to facilitate powerful data retrieval on the Web and Semantic Web. Three categories of Web query languages can be distinguished, according to the format of the data they can retrieve: XML, RDF and Topic Maps. This article introduces the spectrum of languages falling into these categories and summarises their salient aspects. The languages are introduced using common sample data and query types. Key aspects of the query languages considered are stressed in a conclusion

Negative non-ground queries in well founded semantics

Dissertação apresentada na Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa para obtenção do grau de Mestre em Computational LogicThe existing implementations of Well Founded Semantics restrict or forbid the use of variables when using negative queries, something which is essential for using logic programming as a programming language. We present a procedure to obtain results under the Well Founded Semantics that removes this constraint by combining two techniques: the transformation presented in [MMNMH08] to obtain from a program its dual and the derivation procedure presented in [PAP+91] to determine if a query belongs or not to the Well Founded Model of a program. Some problems arise during their combination, mainly due to the original environment for which each one was designed: results obtained in the first one obey a variant of Kunen Semantics and non-ground programs are not allowed (or previously grounded) in the second one. Most of these problems were solved by using abductive techniques, which lead us to observe that the existing implementations of abduction in logic programming disallow the use of variables. The reason for that is the impossibility to evaluate non-ground queries, so it seemed interesting to develop an abductive framework making use of our negation system. Both goals are achieved in this thesis: the capability of solving non-ground queries under Well Founded Semantics and the use of variables in abductive logic programming

Foundations of Rule-Based Query Answering

This survey article introduces into the essential concepts and methods underlying rule-based query languages. It covers four complementary areas: declarative semantics based on adaptations of mathematical logic, operational semantics, complexity and expressive power, and optimisation of query evaluation. The treatment of these areas is foundation-oriented, the foundations having resulted from over four decades of research in the logic programming and database communities on combinations of query languages and rules. These results have later formed the basis for conceiving, improving, and implementing several Web and Semantic Web technologies, in particular query languages such as XQuery or SPARQL for querying relational, XML, and RDF data, and rule languages like the “Rule Interchange Framework (RIF)” currently being developed in a working group of the W3C. Coverage of the article is deliberately limited to declarative languages in a classical setting: issues such as query answering in F-Logic or in description logics, or the relationship of query answering to reactive rules and events, are not addressed