For the purposes of the International Directory Network (IDN), metadata is defined as: "Descriptive information that characterizes a set of quantitative and/or qualitative measurements and distinguishes that set from other similar measurement sets. Controlled keywords are essential within the metadata to provide a normalized discovery for data through 13 sets of controlled keywords, data-related services and tools within the IDN." (L. Olsen)
The metadata used by the IDN is considered to be that set of attributes that are instrumental in helping users to determine if a data set meets their qualifications. The set of attributes (fields) and its associated syntax is known as the Directory Interchange Format (DIF). It has evolved over the years and serves the user community in the discovery of Earth science data.
In addition to the Directory Interchange Format (DIF) standard, the International Directory Network staff works with other groups involved with promoting standards and has cross-mapped its valuable set of fields to other formats to synchronize content.
ISO 19115:2003 defines the schema required for describing geographic information and services. It provides information about the identification, the extent, the quality, the spatial and temporal schema, spatial reference, and distribution of digital geographic data. (iso.org)
UMM is an extensible metadata model which provides a cross-walk for mapping between NASA’s Common Metadata Repository (CMR)-supported metadata standards. Rather than create mappings from each CMR-supported metadata standard to each other, each standard is mapped centrally to UMM, thus reducing the number of translations required for CMR to supported metadata.