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Faceted operations on composed RDF ontologies

Public and private organisations increasingly release their data. The use of these open data can be supported and stimulated by providing considerable metadata, including discovery, contextual and other detailed metadata. This paper argues that faceted indexing of the RDF ontologies, published as linked open data LOD, is an important part of their associated metadata. On the other hand, information needs to be composed from multiple sources to create new information. Through primitive faceted formulas using faceted indexing terms and a list of validity time intervals, we are able to take the union of all RDF ontologies indexed by these terms and are valid in all provided validity time intervals. The resulted RDF ontology is indexed by the provided index terms and has a list of validity time intervals derived by the validity time intervals of the unioned RDF ontologies. By combining both union and intersection operators on primitive faceted formulas, complex expressions can be formed that return a composed RDF ontology, its faceted indexing and validity time intervals. All algorithms are provided along with their complexity.