文档介绍：Query Answering under Non-guarded Rules
in Datalog+/-
Andrea Cal`ı3,2, Gottlob1,2, and Andreas Pieris1
puting Laboratory, University of Oxford, UK
2 Oxford-Man Institute of Quantitative Finance, University of Oxford, UK
3 Department of Information Systems puting, Brunel University, UK
Abstract. In ontology-based data access, an extensional database is
enhanced by an ontology that generates new intensional knowledge which
has to be considered when answering queries. In this setting, tractable
plexity (., complexity . the data only) of query answering
is crucial, given the need to deal with large data sets. A well-known class
of tractable ontology languages is the DL-lite family; however, in DL-
lite it is impossible to express simple and useful integrity constraints
that involve joins. To e this limitation, the Datalog+/- class of
decidable languages uses tuple-generating dependencies (TGDs) as rules,
thus allowing for conjunctions of atoms in the rule bodies, with suitable
limitations to ensure decidability. In particular, sticky sets of TGDs allow
for joins and variable repetition in rule bodies under certain conditions.
In this paper we extend the notion of stickiness by introducing weakly-
sticky sets of TGDs, which also generalize the well-known weakly-acyclic
sets of TGDs. We investigate plexity of query answering under
such language, and in addition we provide plexity results on
weakly-acyclic sets of TGDs. Moreover, we present the novel class of
sticky-join sets of TGDs, which generalizes both sticky sets of TGDs
and so-called linear TGDs, an extension of inclusion dependencies.
1 Introduction
Due to plex knowledge representation needs in today’s information sys-
tems, traditional database systems are being enhanced with advanced reasoning
and query processing features. In the business world, enterprise data reside usu-
ally at relational databases, plex constraints have to