Faceted classification: Orthogonal facets and graphs of foci?

Faceted classification is based on the core ideas that there are kinds or categories of concepts, and that compound, or non elemental, concepts, which are ubiquitous in classification and sub-ject annotation, are to be identified as being constructions of concepts of the different kinds. The categories of concepts are facets, and the individual concepts, which are instances of those facets, are foci. Usually, there are constraints on how the foci can be combined into the compound concepts. What is standard is that any combination of foci is permitted from kind-to-kind across facets, but that the foci within a facet are restricted in their use by virtue of being dependent on each other, either by being exclusive of each other or by bearing some kind of hierarchical relationship to each other. Thus faceted classification is typically considered to be a synthetic classification consisting of orthogonal facets which themselves are composed individually either of exclusive foci or of a hierarchy of foci. This paper addresses in particular this second exclusive-or- hierarchical foci condition. It evaluates the arguments for the condition and finds them not conclusive. It suggests that wider synthetic constructions should be allowed on foci within a facet.