Keywords are words or phrases that describe the metadata resource. They facilitate search, indexing and discovery of metadata, and are the largest single component of many metadata collections, regardless of the dialect.
Using common types to classify keywords is critical for consistent discovery, particularly using faceted searches. Shared vocabularies that include these new types are important contributor to consistent, interoperable metadata. The keyword types in italics are supported by NASA Global Change Master Directory (GCMD) and used in many existing metadata collections.
The UML for the MD_Keywords object includes keyword, type, and thesaurusName fields. A minimum of one keyword field is mandatory. The type field groups keywords into like categories using KeywordTypeCodes and the thesaurusName field provides a citation to the authoritative source of keywords.