Syntax of facets and sources of foci : a review of alternatives

Although the notion of facet occurs in many knowledge organization systems (KOS), the term facet has been used with different meanings and roles over time. Generally, the term suggests the combination of several concepts in order to specify the subject of a document. However, the syntax of such combinations varies considerably, as do the sources from which the possible values of a facet (known as 'foci') can be taken. This paper provides an overview of syntactical alternatives in faceted systems. Concepts can be simply juxtaposed without expressing the relationship between them (free combination); or the relationship can be expressed and link two concepts taken from any part of the scheme (freely faceted systems, phase relationships); or it can be characteristic of only a given basic class and allow it to link to a choice of other concepts according to a facet formula (classical faceted classification, special facets); or it can link any basic class to a choice of auxiliary concepts such as space, time or form (common facets). Foci, in turn, can be taken from any other part of the system, or typically from a certain part, or be defined in the context of the facet itself. When describing a KOS as ‘faceted’, which now seems to be a fashionable attribute, the nature of such ‘facets’ should be made explicit. Finally, the supposed ‘rationalistic’ theoretical basis of facet analysis, as opposed to ‘empirical’ or ‘pragmaticist’, is briefly discussed.