Query Answering over Contextualized RDF/OWL Knowledge with Forall-Existential Bridge Rules: Attaining Decidability using Acyclicity (full version)

TL;DR

This paper addresses query answering over context-rich RDF/OWL knowledge using bridge rules, introducing a decidable class called context-acyclic quad-systems and analyzing their complexity.

Contribution

It defines a new decidable class of quad-systems with forall-existential bridge rules, enabling effective query answering in complex semantic web contexts.

Findings

Decidability is achieved for context-acyclic quad-systems.

Forward chaining is effective for query answering in the proposed class.

Complexity bounds for data and combined scenarios are established.

Abstract

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.