As we have seen in Chapter 7, a thesaurus consists of a systematic display and an alphabetical display, the two being interdependent. In the systematic display the relationships between terms are shown visually by the indentation of terms, so that subordinate and coordinate status are evident from the page layout. In the alphabetical display these relationships between terms are obscured, so must be identified by a system of crossreferences, that is the thesaural relations.

It is easiest to establish the correct relationships by constructing the systematic display, so this is done as a first stage. It is then converted to an alphabetical format when the structure of the vocabulary has been determined.

We shall do this for our model thesaurus by a method known as facet analysis. It should be emphasized that this is not the only method of constructing a thesaurus, but it is a well established and reliable method, underpinned by a rational, scientific theory.

Facet analysis

The idea of facet analysis was conceived by S. R. Ranganathan in the 1920s and 1930s, and was implemented in a library classification scheme, the Colon Classification. The established library classifications of the time tended to be lists of topics likely to occur as the subjects of books, arrived at on a pragmatic basis, and including large numbers of compound classes (such as ‘the pineapple canning industry in Hawaii’, or ‘science and religious belief in 17th century England’). The central notion of facet analysis is that vocabulary tools for subject fields can be better organized by identifying the individual constituent concepts of the subject (and combining them as and when needed), than by detailing all the possible combinations of concepts in a long list of pre-coordinated classes.

The faceted type of vocabulary tool tends to be briefer, more logical, and more flexible than a pre-combined enumeration of compound subjects. It is also closer to the culture of post-coordinate indexing, with the use of relatively simple keywords or descriptors. Although Ranganathan’ methods were initially used to create a library classification for the physical arrangement of documents, the economical structure of the faceted classification makes it very easily turned into a thesaurus.

Fundamental categories

Facet analysis works by applying broad principles of division to the concepts in the subject field to achieve a separation of these into facets, or aspects, of the subject.