Facets, Levels and Semantic Factoring

Knowledge Organization Systems (KOS) can be constructed on the basis of three main kinds of relationships: classical hierarchies; facets; and concepts related in some other relevant way. Among related concepts, of special interest are semantic factors, that is concepts occurring in the definition of a term or class. In an evolutionary perspective, factors can combine, leading to the emergence of a new class of phenomena at a higher integrative level. Recording factors in the schedules of a KOS can make it more sound in ontological terms, and allow for additional functionalities in its application to information retrieval, like query expansion. Some aspects and problems of this are discussed, including of the extent of the semantic network to be considered for each search, and fuzzy relationships with concepts concurring to the definition of terms or classes. Examples are provided from UDC, ILC, and the ISO standard for thesaurus interoperability. It is concluded that facets and semantic factors should be reconsidered as powerful components in KOS development, as well as in KOS representation in the context of the Semantic Web.