tauOWL: A Framework for Managing Temporal Semantic Web Documents Supporting Temporal Schema Versioning

The OWL 2 Web Ontology Language allows defining both schema and instances of ontologies for Semantic Web applications, but lacks explicit support for time-varying ontologies. Hence, knowledge engineers or maintainers of Semantic Web documents have to use ad hoc techniques in order to specify an OWL 2 schema for time-varying instances and to cope with its temporal evolution. In this paper, for a disciplined and systematic approach to the temporal management of OWL 2 ontologies, we propose the adoption of a framework called Temporal OWL 2 (tauOWL), inspired by the Temporal XML Schema (tauXSchema) framework defined for XML data. Hence, tauOWL allows creating a temporal OWL 2 ontology from a conventional (i.e., non-temporal) OWL 2 ontology and a set of logical and physical annotations. Logical annotations identify which elements of a Semantic Web document can vary over time and physical annotations specify how the time-varying aspects are represented in the document. By using annotations to integrate temporal aspects in the traditional Semantic Web, our framework (i) guarantees logical and physical data independence for temporal schemas and (ii) provides a low-impact solution since it requires neither modifications of existing Semantic Web documents, nor extensions to the OWL 2 recommendation and Semantic Web standards. Furthermore, temporal versioning of the schema itself is supported in tauOWL by means of a temporal schema, which is a document that binds the three components of a tauOWL schema to the temporal versions they belong to. In tauOWL, either the conventional schema and the temporal schema can be versioned, by means of two dedicated complete sets of schema change primitives, which are defined in this work. We also illustrate their use and show their impact on OWL 2 instances through an example.