ESDS-RFC-023

Title

Updates to Directory Interchange Format (DIF) Standard

Abstract

This document describes modifications to the Directory Interchange Format (DIF) according to International Directory Network Version 9.8.2 Release Notes, October 2010. The Global Change Master Directory (GCMD) is an implementation of the DIF.

Synopsis

Final Recommendation

The ESDS-RFC-023 Technical Working Group (TWG) has conducted a review of ESDS-RFC-023 – Updates to Directory Interchange Format (DIF) Standard and reached the following conclusion:

That the Standards Process Group should forward to NASA Earth Science Division ESDS-RFC-023 with the recommendation that it be endorsed as a NASA Technical Note.

Recommendation

The TWG bases its recommendation on positive comments from the Earth Science community, including NASA and international DIF users, and an analysis of the following factors in a NASA context:

Strengths: ESDS-RFC-023documents 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.”

History

The GCMD DIF has been widely used for twenty years, both within NASA and internationally, for directory level metadata.  In 2008, the Standards Process Group of NASA’s Earth Science Data Systems Working Groups recommended endorsement of the DIF as a NASA standard for metadata exchange (ESDS-RFC-012).  The DIF schema has evolved over the years, and we expect schema changes to continue as NASA Earth Science data systems begin to adopt ISO metadata standards.  In order to stay current, the SPG and GCMD staff are working together to document minor changes to the 2008 DIF specification via Technical Note RFCs.  If and when the GCMD makes significant changes to the DIF schema, or if the schema becomes significantly different from the 2008 specification over time, we will likely evaluate a new standards track RFC to replace the original DIF Standard RFC (RFC-012), this Technical Note (RFC-023) and any others documenting changes to the DIF.

RFC Overview

ESDS-RFC-023 documents two changes to the DIF schema, for improved compatibility with FGDC CSDGM and ISO 19115 metadata standards:  (1) restructuring of the DIF Summary field to contain two sub-fields, Abstract and Purpose; and (2) the addition of optional sub-fields such as Author and Publication Date to the DIF Reference field.  These changes are reflected in the GCMD Release Notes 9.8.2, the corresponding DIF XML schema, and the docBUILDER tool for DIF authors.