Thesaurus is a collection of terms developed for a database. Each record in the database is usually allocated several thesaurus terms in order to identify the key themes or subjects it covers. A controlled vocabulary is a standardized set of words or phrases used in search tools such as databases and catalogues to aid in document retrieval. In these tools, you often see a controlled vocabulary in the form of 'subject headings' or 'descriptors'. These subject headings are applied to each resource to describe the topic areas of the document. “Controlled vocabulary offers the benefits of consistency, accuracy, and control … which are often lacking in the free-text/natural language approach”.
Different databases use different terms:
Controlled vocabulary terms include subject headings such as MeSH.
see cellular telephones
Controlled term may be ‘distance education’ and articles with the term ‘distance learning’ (as used in many articles by American authors) will not be retrieved.
The use of preferred subject headings and indexing terms allows the grouping together of information sources and that may contain indicative or relevant words in the title or abstract and which would otherwise be difficult to find if only ‘natural language’ terms were used.