Overview
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.
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.
Conceptual Model (UML)
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. Using common types to classify keywords is critical for consistent discovery, particularly using faceted searches.
The MD_KeywordClass object is new with ISO 19115-1. This object was added in order to allow unambiguous specification of keywords from ontologies. MD_Keywords instance with a MD_KeywordClass to provide user-defined categorization of groups of keywords that extend or are orthogonal to the standardized KeywordTypeCodes, and are associated with an ontology that allows additional semantic query processing.
The thesaurus citation specifies a collection of instances from some ontology, but is not an ontology. It might be a list of places that include rivers, mountains, counties and cities. There might be a Laconte county, the city of Laconte, the Laconte River, and Mt. Laconte; when searching it is useful for the user to be able to restrict the search to only rivers.
Implementation (XML)
Usage
ECHO to ISO Keyword Mapping
Overview
Content Tools