This attribute is used with two different definitions.
- The most common is the name of the thesaurus, ontology, or organization that established a particular group of keywords, for example, “MESH”, “ISO-463”, “IEEE”, “author-generated”, “ICD9-codes”, etc.
- The second usage describes the type of keyword
for some of the more unusual keyword groups (for
for keywords that
are grouped into a hierarchy,
keywords that contain an abbreviation and its expansion,
or “code” for
keywords that contain a code
and its text but where the source of the codes is unknown).
|Text, numbers, or special characters||The source of keywords. This may be an organization (such as “IEEE”) or the name of a thesaurus, subject index, or ontology (such as “MESH”).|
|Restriction: This is an optional attribute; there is no default.|