FAQ - Unique Identifiers
Unique Metadata Identifiers
Metadata identifiers provide a mechanism for uniquely identifying metadata records and resources. Unique identifiers are character strings associated with a single entity and are required to be unique. Identifiers increase the efficiency and accuracy of metadata by enabling direct and reliable access to individual resources. As the number of geospatial data resources rapidly increases, the ability to identify and locate resources becomes more complex and the role of unique identifiers more critical.
Many agencies have implemented a standardized approach for the assignment of unique identifiers to the resources produced by the agency. Agencies that have not implemented the assignment of unique identifiers are strongly encouraged to implement unique identifiers in accordance with the World Wide Web Consortium (W3C) and Open Geospatial Consortium (OGC) Best Practices. W3C and OGC recommend the use of a Uniform Resources Identifier (URI) - an IETF/W3C standard scheme for treating resource identifiers as globally unique and persistent, even when the resource ceases to exist or becomes unavailable.
Metadata Record Identifier
The value that uniquely identifies a metadata record. This identifier is assigned and maintained by the custodian of the metadata record.
<gmd:fileIdentifier> <gco:CharacterString>**Unique Identifier**</gco:CharacterString> </gmd:fileIdentifier>
The value that uniquely identifies a resource. Citations are used throughout ISO to provide information about scientific articles, reports, books, user guides, manuals, and other sources that refer to or provide cite-able information about the resource (a dataset, service).
<gmd:CI\_Citation> <gmd:identifier> <gmd:MD\_Identifier> <gmd:CI\_Citation> <gmd:code>Unique Identifier</gmd:code>
FGDC Technical Guidance: Data.gov and The GeoPlatform Metadata Recommendations
National Oceanic and Atmospheric Administration example FileIdentifier.
NOAA ISO Explorer Home Page and CI_Citation