What is a controlled vocabulary?
A controlled vocabulary is an established list of standardized terms used for both indexing and retrieval of information. An example of a controlled vocabulary is subject headings used to describe library resources. A controlled vocabulary ensures that a subject will be described using the same preferred term each time it is indexed, making it easier to find all information about a specific topic during the search process (e.g., Canadian Subject Headings or the Répertoire de vedettes-matière (RVM)).
Who uses a controlled vocabulary and who decides on the terms?
Content creators use terms from a controlled vocabulary to describe the information contained in their documents (indexing). As a result, Canadians have quicker, focused access to the government information they need. Preferred terms are terms selected from amongst a group of synonyms to be the authorized descriptors.
Searchers use controlled vocabularies by selecting terms from a thesaurus or list of preferred terms, then searching websites or databases for those terms that suit their information needs.
Specialists, such as librarians, make decisions about which terms should be designated as "preferred" in a controlled vocabulary. To do this, they look at the terminology used in the information resources. They also consult with other specialists and researchers working in the subject field. Preferred terms will be the ones most commonly used in the discipline.
Not all situations call for using controlled vocabulary. It is labour-intensive and time-consuming to develop a controlled vocabulary system. Controlled vocabulary is most valuable for scholarly or technical materials that result from extensive research.
Why use a controlled vocabulary?
Assigning terms from a controlled vocabulary facilitates access to government information for all Canadians by allowing focusing of search results on Government of Canada search engines.
For further information, consult the Government of Canada Metadata Implementation Guidelines for Web Resource Discovery
What controlled vocabulary do I use?
Treasury Board's Standard on Metadata requires that terms from a controlled vocabulary be used as values in the subject metadata element when describing Web resources.
The controlled vocabulary used must be registered with Library and Archives Canada or the Dublin Core Metadata Initiative. More specifically, the standard identifies the Government of Canada Core Subject Thesaurus, managed by Library and Archives Canada, as the preferred source of controlled vocabulary for that purpose.
Consult your departmental library and information management experts to determine if a controlled vocabulary or formal classification scheme is already in use in your department. The default vocabulary, if no departmental scheme is available, is the Government of Canada Core Subject Thesaurus (CST).
In any case, for interoperability purposes, it is highly recommended that one or more terms from the CST be selected as the content for "dc.subject". Other registered vocabularies and/or classification schemes may additionally be used.
If the terms you need to describe your information are not in the CST, or if your subject area is not well represented, please contact the CST Editor.
If the terminology of the CST is too broad or otherwise unsuitable for use as descriptors for your information, consider using a different controlled vocabulary. Consult the advice in the Guide to the Development and Maintenance of Controlled Vocabularies in the Government of Canada. If all else fails, consult the Metadata Coordinator at Library and Archives Canada for advice.
How do I implement controlled vocabulary on our Web site?
Consult the Indexing Federal Government Web Pages: Guidelines For the Development of an Indexing Policy page for general implementation advice.
If you will be using the Government of Canada Core Subject Thesaurus (CST), see the section of the CST Web site called Indexing with the Thesaurus.
Which Web pages are involved?
Guidance on how to identify key departmental resources for the purposes of meta tagging is available in the Treasury Board Information Management Standard (TBITS) 39.1.