As we have already seen in the introduction and in the examples, a thesaurus can take a number of forms, from a simple keyword list to a fully integrated systematic and alphabetic display with all the detailed relationships between terms carefully worked out. Although the simple keyword list may still be sufficient for a very small document collection, in the majority of cases the needs of users are better served by having a properly constructed system, based on logical principles, since this is in the long run easier to update and maintain, and is more compatible with the machine management of the thesaurus.

In this chapter we shall consider the various parts of the thesaurus as it is laid out on the page or screen. You should remember that although there are various national and international standards for thesaurus construction, these differ in some respects, and in practice, individual thesauri may use a local style different from any format proposed in the standards.

Most modern thesauri consist of two elements: a systematic structure where the relationships between terms can be seen in a visual display; and the alphabetical display, where the terms are listed in A–Z order, each with cross-references to other terms related in some way.

The systematic display

The systematic display is sometimes not given prominence in the published tool, and in older thesauri it may provide no more than a summarization of the topics covered. Nevertheless, it can play a vital part in designing the thesaurus and establishing relationships. A browsing tool of this sort can also be of great use to the indexer (and also to the end-users, although they are less likely to be aware of it) in providing a map of the subject. The capacity to scan the broad subject structure, to see which subjects are represented, and to select appropriate descriptors, can often be more easily achieved in a systematic display than in the distributed vocabulary of the A–Z list.

For example, in the section for dentistry in a hypothetical medical thesaurus, part of the systematic display might look like this:

The systematic display brings together a number of terms which are widely scattered in the A–Z format (teeth, dental techniques, crown, extraction, etc.), and also gives a sense of the number and range of terms in the vocabulary which are available for indexing in this particular subject area.