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 at the collection level. From its inception in the late 1980’s as a way to document and exchange information on scientific data to its implementation in NASA's 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. GCMD metadata records are now maintained in the Common Metadata Repository (CMR), and the DIF is one of several supported formats for submitting metadata to CMR.

The DIF, the ECHO metadata model, and the ISO 19115 standards for science metadata formed the basis for NASA's Unified Metadata Model (UMM) used by CMR.

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. DIF 10 is a supported metadata format for submitting collection level metadata to CMR.

DIF 10.2 is the current operational version and DIF 10.3 is upcoming in 2019.

Current Schema Definition DIF 10 XML Schema Definition (XSD) Documents
2010 Update Document Updates to Directory Interchange Format (DIF) Standard (ESDS-RFC-023)
2008 Specification Document Directory Interchange Format (DIF) Standard (ESDS-RFC-012)
User Resources DIF Documents and Tools GCMD Keywords Community Forum—An area for discussion of topics related to the GCMD Keywords.

NASA Earth Science Community Recommendations for Use

The following recommendations for use were garnered from community review when the DIF was originally submitted as a proposed standard for NASA Earth Science Data Systems in 2008 and updated in 2010. The DIF remains a recommended standard for collection level metadata exchange, particularly for submission of metadata to CMR, and for exchange of metadata records within the International Directory Network (IDN).

NASA Earth Science Community Recommendations for Use (2010)

Strengths

ESDS-RFC-023 documents 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) metadata standards, 19115-1 (Geographic information—Metadata—Part 1: Fundamentals) and 19115-2 (Geographic information—Metadata—Part 2: Extensions for imagery and gridded data). 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 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 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. It is not designed for use as inventory (granule) 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 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 Technical Working Group thus recommends its endorsement by ESO as an Earth Science Data Systems Standard.

Last Updated: Sep 17, 2019 at 12:04 PM EDT