User needs determine what functions should be provided, and different functions require different structures. - Brian Campbell Vickery

Classification in its simplest terms, means putting together things or ideas that are alike, and keeping separate those that are different.

The structural tools developed by the profession – hierarchical classifications, facets, thesaural relations, topic maps, the predicates used in ontology – will still be of use, provided that they can in each case pass a test of utility.

Facet analysis results in more varied, multidimensional relationships, at least in theory, better reflecting the complexity of subject knowledge