What is a Thesaurus?
A thesaurus represents a collection of organised knowledge, often based on
an abstract classification scheme, which provides a "map" of some subject
domain. It is used by professional indexers as a source of controlled
language document descriptors, and by intermediaries and expert users
as an aid to the precise specification of queries.
A typical entry from a printed thesaurus
displays details of one term, and its relationships
with other terms. Terms are often phrases consisting of two or more
words. The relationships defined are:
- Equivalence (UF/U). When indexing or searching, the
preferred term is to be "used for" one or more lead-in
terms, which are considered to be its synonyms.
- Hierarchical (BT/NT). A "narrower term" is more specific in
meaning and so further down the tree; a "broader term" is more general in
meaning and therefore higher up the tree.
- Associative (RT). A "related term" is one which is closely
linked in meaning or subject area, but neither a synonym nor
hierarchically related.
The broader / narrower term relationship partitions the thesaurus into a
number of separate hierarchies, each with its own top term. (See
a typical hierarchical display from a printed
thesaurus.) More generally, a thesaurus can be considered as a large
semantic net to be represented in machine-readable form. Given a
particular query term as starting point, users may navigate through the
net, identifying additional terms to enhance their queries.