Using Hybrid Knowledge Bases for Meta-reasoning over OWL 2 QL.

Metamodeling refers to scenarios in ontologies in which class-es and roles can be members of classes or occur in roles. This is a desirable modelling feature in several applications, but allowing it without restrictions is problematic for several reasons, mainly because it causes undecidability. Therefore, practical languages either forbid metamodeling explicitly or treat occurrences of classes as instances to be semantically different from other occurrences, thereby not allowing metamodeling semantically. Several extensions have been proposed to provide metamodeling to some extent. This paper focuses on the extension called Metamodeling Semantics (MS) over OWL 2 QL and the Metamodeling Semantic Entailment Regime (MSER). Reasoning over the latter requires more than an OWL 2 QL reasoner, and in the past a solution that transforms MSER to query answering over Datalog has been proposed. In this paper, we investigate the use of Hybrid Knowledge Bases for MSER. Hybrid Knowledge Bases have rule and ontology components, and we provide translations that keep some portion of the original metamodeling ontology in the ontology part. This is accompanied by a translation of SPARQL queries (including metaqueries) to queries over the Hybrid Knowledge Base. The target language is compatible with the hybrid reasoner called HEXLite-owl-api-plugin, allowing for an effective reasoning tool over metamodeling ontologies, which we evaluate experimentally.