In previous chapters we have looked at some of the different kinds of structure to be found in the thesaurus and related subject tools, and the purposes to which the thesaurus can be put. Other aspects of the thesaurus include the scope and range of the vocabulary, and the sort of material to which it is intended to be applied.

General and special thesauri

General thesauri: UNESCO and BSI Root

The thesaurus is unlike the bibliographic classification scheme, and more like contemporary taxonomic tools, in that it is more usually designed for a specific and limited subject field. Whereas several large general classification schemes and subject heading lists exist, there are no completely general thesauri. However, there are a few that cover a wide range of subjects. The two best known of those that are available are the UNESCO Thesaurus and the British Standard Institution's Root Thesaurus.

Although they are widely regarded as being general in scope, in reality neither deals with the whole of human knowledge in the way that, for example, the Dewey Decimal Classification does. The University of London Computing Centre hosts a browsable version of the UNESCO Thesaurus at www.ulcc.ac.uk/unesco/, of which it states:

This clearly relates to the economic, social, and cultural subjects which are UNESCO's remit. Although the thesaurus does contain some vocabulary for the sciences, this is largely related to economic and social aspects of those subjects, and there is no detailed terminology for, say, technology or the pure sciences.

The BSI Root Thesaurus was developed for BSI's in-house indexing of its own standards, and its descriptors are now entered into the BSI database available for online searching for British Standards. The scope of the thesaurus is potentially very broad, but, in practical terms, has something of a bias towards the scientific and technical since those are the subjects in which standards predominate.