This attribute is used with two different definitions:
- The most common is to name 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 example, “hierarchical” for
keywords that are grouped into a hierarchy, “abbreviations” for 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
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 attribute may be specified if the element is used.