Vocabularies
Thesauri, restricted or controlled vocabularies and language taxonomies are a way to describe and organise documents or web pages into logical, ordered groups of relationships, based on their subject, using a set of agreed terms or categories.
Thesauri, vocabularies and taxonomies can be created for a particular subject area or organisation. These specific vocabularies are then used to describe the subject and contents of documents.
A thesaurus is constructed to identify relationships within and between concepts.
A thesaurus normally adhers to a set of internationally recognised standards that provide guidance on the format and structure of terms. These standards are ANSI-NISO Z39.19-1993 and ISO 2788.
Consistency of Description
The use of vocabularies is aimed at creating consistency in the way the subject of a document or web page is described.
Assists in Information Retrieval
Using a vocabulary assists in the consistent categorisation of information with a subject area or organisation. This then aids information retrieval, because in a search the use of a vocabulary term will return documents related to the same subject.
Use Multiple Vocabularies
Of course, language can be ambiguous and different people will tend to prefer particular terms over others. This may mean that multiple vocabularies are used and comparable terms from the different vocabularies are used to describe the same document content or subject.
Thesauri, restricted vocabularies and language taxonomies can be used to limit the scope of a search, thus reducing the amount of irrelevant documents returned.