WHAT IS A THESAURUS?

• For writers, it is a tool like Roget's — one with words grouped and classified to help select the right word to convey a specific nuance of meaning.
• For indexers and searchers, it is an information storage and retrieval tool: a listing of words and phrases authorized for use in an indexing system, together with relationships, variants and synonyms, and aids to navigation through the thesaurus.

For more information on what a thesaurus is and what it contains, see: National Information Standards Institute. American National Standard Guidelines for the Construction, Format, and Management of Monolingual Thesauri. Bethesda, MD: NISO Press, 1994. (ANSI/NISO Z39.19-1993).

WHEN DO I NEED A THESAURUS?

• For a single back of the book index, the terms derived from the text, plus the cross-references that are added, represent the "thesaurus" for that index, so developing a separate thesaurus probably isn't worthwhile. However, you may find an existing thesaurus helpful for terminology questions.
• For a large index, one that is ongoing, or one where multiple indexers will be involved, a thesaurus is almost a necessity. There is no way to maintain consistency over time or across indexers without one.

CAN I USE AN EXISTING THESAURUS?

• Almost all existing published thesauri have been developed to serve the needs of a particular database. Unless your index is of exactly the same scope and level, an existing thesaurus is unlikely to meet your needs precisely.
• However, there may be an existing thesaurus that you can adapt or even use as is, and it's worth looking.

Different fields vary in how well they are served by thesauri. With the exception of the Art and Architecture Thesaurus, science and technology are far better covered than the humanities, with the social sciences falling somewhere in between.

And if the problem weren't complicated enough, just finding out if a thesaurus exists for a subject area can be a major challenge. The Thesaurus Guide, 2nd ed., 1992, published by the Commission of the European Communities, is immense, but very incomplete. Another possibility is to check out databases in the subject area, and find out if they have published thesauri.

The above information was written by Jessica Milstead specifically for use on the ASI Web site. Copyright 1996, Jessica Milstead.

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