Working with Multiple Ontologies on the Semantic Web

Abstract

The standardization of the second generation Web Ontology Language, OWL, leaves a crucial issue for Web-based ontologies unsatisfactorily resolved: how to represent and reason with multiple distinct, but linked, ontologies. OWL provides the owl:imports construct which, roughly, allows Web ontologies to include other Web ontologies, but only by merging all the linked ontologies into a single logical “space.” Recent work on multidimensional logics, fusions and other combinations of modal logics, distributed and contextual logics, and the like have tried to find formalisms wherein knowledge bases (and their logic) are kept more distinct but yet affect each other. These formalisms have various degrees of robustness in their computational complexity, their modularity, their expressivity, and their intuitiveness to modelers. In this paper, we explore a family of such formalisms, grounded in $\mathcal{E}$-connections as extensions to OWL, with emphasis on a novel sub-formalism that seems very straightforward to implement on existing tableau OWL reasoners, as witnessed by our implementation of this formalism in the OWL reasoner Pellet. We discuss how to integrate those formalisms into OWL, as well as some of the issues that modelers have to face when using such formalisms in the context of a large number of heterogeneous, independently developed, richly interconnected ontologies that we expect to be the norm on the Semantic Web.