2 research outputs found
Query Answering over Contextualized RDF/OWL Knowledge with Forall-Existential Bridge Rules: Attaining Decidability using Acyclicity (full version)
The recent outburst of context-dependent knowledge on the Semantic Web (SW)
has led to the realization of the importance of the quads in the SW community.
Quads, which extend a standard RDF triple, by adding a new parameter of the
`context' of an RDF triple, thus informs a reasoner to distinguish between the
knowledge in various contexts. Although this distinction separates the triples
in an RDF graph into various contexts, and allows the reasoning to be decoupled
across various contexts, bridge rules need to be provided for inter-operating
the knowledge across these contexts. We call a set of quads together with the
bridge rules, a quad-system. In this paper, we discuss the problem of query
answering over quad-systems with expressive forall-existential bridge rules. It
turns out the query answering over quad-systems is undecidable, in general. We
derive a decidable class of quad-systems, namely context-acyclic quad-systems,
for which query answering can be done using forward chaining. Tight bounds for
data and combined complexity of query entailment has been established for the
derived class
Query Answering over Contextualized RDF/OWL Knowledge with Forall-Existential Bridge Rules: Decidable Finite Extension Classes (Post Print)
The proliferation of contextualized knowledge in the Semantic Web (SW) has
led to the popularity of knowledge formats such as \emph{quads} in the SW
community. A quad is an extension of an RDF triple with contextual information
of the triple. In this paper, we study the problem of query answering over
quads augmented with forall-existential bridge rules that enable
interoperability of reasoning between triples in various contexts. We call a
set of quads together with such expressive bridge rules, a quad-system. Query
answering over quad-systems is undecidable, in general. We derive decidable
classes of quad-systems, for which query answering can be done using forward
chaining. Sound, complete and terminating procedures, which are adaptations of
the well known chase algorithm, are provided for these classes for deciding
query entailment. Safe, msafe, and csafe class of quad-systems restrict the
structure of blank nodes generated during the chase computation process to be
directed acyclic graphs (DAGs) of bounded depth. RR and restricted RR classes
do not allow the generation of blank nodes during the chase computation
process. Both data and combined complexity of query entailment has been
established for the classes derived. We further show that quad-systems are
equivalent to forall-existential rules whose predicates are restricted to
ternary arity, modulo polynomial time translations. We subsequently show that
the technique of safety, strictly subsumes in expressivity, some of the well
known and expressive techniques, such as joint acyclicity and model faithful
acyclicity, used for decidability guarantees in the realm of forall-existential
rules