subject — One of a group of terms describing the subject matter of a document.


subject ::=


Common attributes and common linking attributes.

Additional attributes:

  • weight


A subject categorizes or describes the topic of a document, or section of a document. In DocBook, a subject is defined by the subjectterms that it contains.

Subject terms should be drawn from a controlled vocabulary, such as the Library of Congress Subject Headings. If an outside vocabulary is not appropriate, a local or institutional subject set should be created.

The advantage of a controlled vocabulary is that it places the document into a known subject space. Searching the subject space with a particular subject term will find all of the documents that claim to have that subject. There’s no need to worry about terms that are synonymous with the search item, or homophones of the search term.

All of the subjectterms in a subject should describe the same subject, and be from the same controlled vocabulary.

Processing expectations

May be formatted inline or as a displayed block, depending on context. Subjects are rarely displayed to a reader. Usually, they are reserved for searching and retrieval purposes.

Unlike keywords, which may be chosen freely, subject terms should come from a controlled vocabulary.

In order to ensure that typographic or other errors are not introduced into the subject terms, they should be compared against the controlled vocabulary by an external process.


Common attributes and common linking attributes.


Specifies a ranking for this subject relative to other subjects in the same set


These elements contain subject: subjectset.


The following elements occur in subject: subjectterm.

See Also

Related elements: keyword, keywordset, subjectset, subjectterm.