Abstract

Faceted knowledge organization systems have sophisticated logical structures, making their representation as linked data a demanding task. The term facet is often used in ambiguous ways: while in thesauri facets only work as semantic categories, in classification schemes they also have syntactic functions. The need to convert the Integrative Levels Classification (ILC) into SKOS stimulated a more general analysis of the different kinds of syntactic facets, as can be represented in terms of RDF properties and their respective domain and range. A nomenclature is proposed, distinguishing between common facets, which can be appended to any class, that is, have an unrestricted domain; and special facets, which are exclusive to some class, that is, have a restricted domain. In both cases, foci can be taken from any other class (unrestricted range: free facets), or only from subclasses of an existing class (parallel facets), or be defined specifically for the present class (bound facets). Examples are given of such cases in ILC and in the Dewey Decimal Classification (DDC).