Documenting Keywords

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. Keywords usually come from shared vocabularies in order to encourage consistency across metadata collections. Keywords can support text searches as well as facet searches.

GCMD

NASA GCMD keyword vocabularies ensure that metadata is described in a consistent manner. There are seven sets of controlled keywords in the GCMD directory: (1) Earth Science, (2) Data Services, (3) Data Centers, (4) Locations, (5) Instrument/Sensors, (6) Platforms/Sources, and (7) Projects.

GCMD Keywords are organized into hierarchical groups ranging from general Category Keywords to very specific Variable Level Keywords. The GCMD keywords include the following hierarchy levels; Category > Topic > Term > Variable Level 1 > Variable Level 2 > Variable Level 3 > Detailed Variable. Earth Science Keywords, also know as 'Theme' Keywords are highly recommended by most metadata dialects.

EARTH SCIENCE > ATMOSPHERE > CLOUDS > CLOUD DYNAMICS > MOISTURE FLUX > DOWNWARD MOISTURE FLUX

NASA Dialects

GCMD Keywords are required or recommended in the following NASA documentation dialects:

• Directory Interchange Format (DIF)
• Earth Observing System Clearinghouse (ECHO)
• Service Entry Resource Format (SERF)
• Earth Observation System Data and Information Core System (ECS

Below are examples of Keyword documentation in each of these dialects.

ECHO

<ScienceKeyword>
    <CategoryKeyword>EARTH SCIENCE</CategoryKeyword>
    <TopicKeyword>ATMOSPHERE</TopicKeyword>
    <TermKeyword>ATMOSPHERIC CHEMISTRY</TermKeyword>
    <VariableLevel1Keyword>
        <Value>OXYGEN COMPOUNDS</Value>
        <VariableLevel2Keyword>
            <Value>OZONE</Value>
            <VariableLevel3Keyword>Keyword#3</VariableLevel3Keyword>
        </VariableLevel2Keyword>
    </VariableLevel1Keyword>
</ScienceKeyword>

DIF

<Parameters>
        <Category>EARTH SCIENCE</Category>
        <Topic>ATMOSPHERE</Topic>
        <Term>ATMOSPHERIC CHEMISTRY</Term>
        <Variable_Level_1>OXYGEN COMPOUNDS</Variable_Level_1>
        <Variable_Level_2>OZONE</Variable_Level_2>
        <Variable_Level_3>Keyword#3</Variable_Level_3>
        <Detailed_Variable>Uncontrolled Keyword</Detailed_Variable>
    </Parameters>

ISO

The MD_Keyword object in ISO 19115-1.

<mri:descriptiveKeywords>
  <mri:MD_Keywords>
     <mri:keyword/>         // Keyword
     <mri:type/>            // Type of Keyword (Theme, Instrument, Place etc)
     <mri:thesaurusName/>   // Reference to the controlled vocabulary keyword source (GCMD)
     <mri:keywordClass/>    // User-defined categorization of groups of keywords
  </mri:MD_Keywords>
</mri:descriptiveKeywords>

As noted above GCMD includes 7 Keyword Set Categories. ISO 19115-1 includes 15 Keyword Type Categories. The table below provides a reference list and mapping of GCMD and ISO Keyword Types.

ISO Keyword Types	GCMD Keyword Sets
discipline
place	Locations
statum
temporal
theme	Earth Science
dataCentre	Data Centers
featureType
instrument	Instrument/Sensors
platform	Platforms/Sources
process
project	Projects
service	Data Services
product
subTopicCategory
taxon

Crosswalks

Concept	Description	Dialect (Fit) Paths
Keyword	A word or phrase that describes some aspect of a resource. Can be one of several types. Note: The general identification keywords usually have a type of "theme" and are refered to as "theme keywords". Other types and vocabularies are used for other information. Service Entry Resource Format (SERF) requires a Science and a Service GCMD Keyword. This concept is called "Subject" in the CSW Specification.	DIF (1) /dif:DIF/dif:Parameters/dif:Category DIF (1) /dif:DIF/dif:Parameters/dif:Topic DIF (1) /dif:DIF/dif:Parameters/dif:Term DIF (1) /dif:DIF/dif:Parameters/dif:Variable_Level_1 DIF (1) /dif:DIF/dif:Parameters/dif:Variable_Level_2 DIF (1) /dif:DIF/dif:Parameters/dif:Variable_Level_3 DIF (1) /dif:DIF/dif:Parameters/dif:Detailed_Variable ECHO (1) /*/echo:ScienceKeywords/echo:ScienceKeyword/echo:CategoryKeyword ECHO (1) /*/echo:ScienceKeywords/echo:ScienceKeyword/echo:TopicKeyword ECHO (1) /*/echo:ScienceKeywords/echo:ScienceKeyword/echo:TermKeyword ECHO (1) /*/echo:ScienceKeywords/echo:ScienceKeyword/echo:VariableLevel1Keyword/echo:Value ECHO (1) /*/echo:ScienceKeywords/echo:ScienceKeyword/echo:VariableLevel2Keyword/echo:Value ECHO (1) /*/echo:ScienceKeywords/echo:ScienceKeyword/echo:VariableLevel3Keyword ECHO (1) /*/echo:ScienceKeywords/echo:ScienceKeyword/echo:DetailedVariableKeyword ECS (1) /*/ecs:DisciplineTopicParameters/ecs:DisciplineKeyword ECS (1) /*/ecs:DisciplineTopicParameters/ecs:TopicKeyword ECS (1) /*/ecs:DisciplineTopicParameters/ecs:TermKeyword ECS (1) /*/ecs:DisciplineTopicParameters/ecs:VariableKeyword SERF /serf:SERF/serf:Keyword FGDC (1) /fgdc:metadata/fgdc:idinfo/fgdc:keywords/fgdc:theme/fgdc:themekey ISO (1) /*/gmd:identificationInfo/*/gmd:descriptiveKeywords/gmd:MD_Keywords[gmd:type/gmd:MD_KeywordTypeCode='theme']/gmd:keyword/gco:CharacterString ISO-1 /mdb:MD_Metadata/mdb:identificationInfo/*/mri:descriptiveKeywords/mri:MD_Keywords[mri:type/mri:MD_KeywordTypeCode='theme']/mri:keyword/gco:CharacterString
Keyword Type	Methods used to group similar keywords	ISO /*/gmd:identificationInfo/*/gmd:descriptiveKeywords/gmd:MD_Keywords/gmd:type/gmd:MD_KeywordTypeCode ISO-1 /mdb:MD_Metadata/mdb:identificationInfo/*/mri:descriptiveKeywords/mri:MD_Keywords/mri:type/mri:MD_KeywordTypeCode
Keyword Vocabulary	If you are following a guideline or using a shared vocabulary for the words/phrases in your "keywords" attribute, put the name of that guideline here. Note: DIF, ECHO and ECS require that theme keywords come from the Global Change Master Directory list.	ISO /*/gmd:identificationInfo/*/gmd:descriptiveKeywords/gmd:MD_Keywords[gmd:type/gmd:MD_KeywordTypeCode='theme']/gmd:thesaurusName/gmd:CI_Citation/gmd:title/gco:CharacterString ISO-1 /mdb:MD_Metadata/mdb:identificationInfo/*/mri:descriptiveKeywords/mri:MD_Keywords[mri:type/mri:MD_KeywordTypeCode='theme']/mri:thesaurusName/cit:CI_Citation
Keyword Vocabulary Citation	Name of the formally registered thesaurus or a similar authoritative source of keywords.	ISO /*/gmd:identificationInfo/gmd:MD_DataIdentification/gmd:descriptiveKeywords/gmd:MD_Keywords/gmd:thesaurusName/gmd:CI_Citation ISO /*/gmd:identificationInfo/srv:SV_ServiceIdentification/gmd:descriptiveKeywords/gmd:MD_Keywords/gmd:thesaurusName/gmd:CI_Citation ISO-1 /mdb:MD_Metadata/mdb:identificationInfo/mri:MD_DataIdentification/mri:descriptiveKeywords/mri:MD_Keywords/mri:thesaurusName/cit:CI_Citation ISO-1 /mdb:MD_Metadata/mdb:identificationInfo/srv:SV_ServiceIdentification/mri:descriptiveKeywords/mri:MD_Keywords/mri:thesaurusName/cit:CI_Citation
Keyword Ontology Citation	Reference that binds the keyword class to a formal conceptualization of a knowledge domain for use in semantic processing.	ISO-1 /mdb:MD_Metadata/mdb:identificationInfo/mri:MD_DataIdentification/mri:descriptiveKeywords/mri:MD_Keywords/mri:keywordClass/mri:MD_KeywordClass/mri:ontology/cit:CI_Citation ISO-1 /mdb:MD_Metadata/mdb:identificationInfo/srv:SV_ServiceIdentification/mri:descriptiveKeywords/mri:MD_Keywords/mri:keywordClass/mri:MD_KeywordClass/mri:ontology/cit:CI_Citation

xPath Note: The xPaths included in this table use several wildcards. // means any path, so //gmd:CI_ResponsibleParty indicates a gmd:CI_ResponsibleParty anywhere in an XML file. /*/ indicates a single level with several possible elements. This usually indicates one of several concrete realizations of an abstract object. For example /*/gmd:identificationInfo could be gmd:MD_Metadata/gmd:identificationInfo or gmi:MI_Metadata/gmd:identificationInfo and gmd:identificationInfo//*/gmd:descriptiveKeywords could be gmd:identificationInfo/gmd:MD_DataIdentification/gmd:descriptiveKeywords or gmd:identificationInfo/srv:SV_ServiceIdentification/gmd:descriptiveKeywords.