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  2. Standards, Requirements and References
  3. Directory Interchange Format (DIF) Standard

Directory Interchange Format (DIF) Standard

Summary

This document defines the Directory Interchange Format (DIF) content metadata, a specific set of attributes for describing Earth science data. From its conception in the late 1980’s as a way to document and exchange information on scientific data to its implementation in the Global Change Master Directory (GCMD), the DIF has evolved to serve the user community in the discovery, access and use of Earth science and related data.

Status

The Directory Interchange Format (DIF) Standard is an approved standard recommended for use in NASA Earth Science Data Systems in September 2008. In 2010, updates to the DIF standard were approved. As of August, 2016, DIF 10 is the most recently recommended version.

Current specification DIF 10 web-based documentation
2010 Update Document Updates to Directory Interchange Format (DIF) Standard

2008 Specification Document

Directory Interchange Format (DIF) Standard

User Resources

docBUILDER (GCMD tool for writing DIFs)

GCMD Keywords Community Forum Home

NASA Earth Science Community Recommendations for Use (2010)

Strengths

ESDS-RFC-023 documents recent changes to the DIF schema, intended to enhance interoperability with the Federal Geographic Data Committee (FGDC)Content Standard for Digital Geospatial Metadata (CSDGM) and the International Organisation for Standardisation (ISO) 19115 metadata standards. The DIF itself is already a NASA-endorsed metadata standard (ESDS-RFC-012). Earth Science community comments were all positive. Said one,"This RFC will clearly help integrating data management systems and should be endorsed."

Weaknesses

One commenter notes a perceived weakness: “It looks like, in this community, the separation of purpose out of an abstract is standard. But in normal usage, abstract may likely include purpose.” However, the separate abstract and purpose fields were created specifically to conform to FGDC and ISO metadata specifications.

Applicability

As NASA Earth Science Data Systems move toward adopting ISO metadata standards, closer alignment of our existing metadata standards is welcome. In the words of another commenter, “There will never be only one way of addressing the interoperability issue and DIF has a clear advantage in that it is lightweight and easy to implement and benefit from contrary to ISO standards.”

Limitations

Additional DIF schema changes, beyond the two documented here, will be needed for full ISO compatibility.

Overall, reviewers were pleased with the updates to the DIF schema, and found that the RFC documentation was clear and helpful: “For these minor changes an endorsement is a no-brainer.”

NASA Earth Science Community Recommendations for Use (2008)

Strengths

The DIF is a mature specification. It was first developed in 1987, was chosen by the Committee on Earth Observation Satellites (CEOS) International Directory Network (IDN), and has been used by the NASA GCMD as the means of metadata exchange. The DIF continues to be actively used and maintained by a large variety of organizations, both as a means of interaction with the GCMD as well as for other purposes, including internal data management. The DIF metadata model is compatible with the ISO 19115 metadata model.

Weaknesses

While the DIF is compatible with ISO 19115, there is a feeling among some metadata providers that the DIF should be superseded by ISO 19115.

Applicability

The DIF is meant to contain collection level metadata for Earth science data sets. It is not designed for use as granule, or inventory level metadata. The DIF is primarily a metadata interchange format. Data holders often manage metadata in different internal formats, choosing to export and import metadata in DIF format when interchanging metadata with external organizations, primarily the GCMD.

Limitations

Since DIF is not suited directly as an inventory level metadata format, some data holders perceive this as a limitation. They would prefer to be able to use the same format for inventory level data.

Overall, the DIF is a widely implemented and widely deployed specification that provides a standard way of storing and exchanging Earth science metadata. The ESDS-RFC-012 TWG thus recommends its endorsement by the SPG as an Earth Science Data Systems Standard.

Last Updated: Sep 19, 2017 at 3:00 PM EDT