Before metadata became a ubiquitous buzzword, a descriptive and
standardized format for exchanging information about scientific
data sets was conceived and implemented. The Directory Interchange
Format, the DIF, was the product of an Earth Science and Applications
Data Systems Workshop (ESADS) held February 24-26, 1987 on catalog
interoperability (CI). The workshop recommended that a "...first
step towards data system interoperability, Catalog Interoperability
(CI), the ability to find information about data held at other sites...",
In the summer of 1987, the Catalog Interoperability Working Group
(consisting of several U.S. Federal and international agencies)
defined the type of information and level of detail that would be
contained by the DIF. The DIF structure was "frozen" on September
18, 1987, and the population of NASA's Master Directory (NMD) prototype
commenced. By December 1987, over 100 DIF entries were available
in the prototype NMD database. After several demonstrations, workshops,
and feedback from the scientific community, the Directory Interchange
Format (DIF) was formally approved and adopted by a CI science advisory
group at a CI workshop in 1988.
In 1989, the Committee on Earth Observation Satellites (CEOS)
Data Working Group (DWG) began attending the CI Workshop meetings
and provided valuable feedback on the DIF structure. The CEOS International
Directory Network (IDN) was soon established under the auspices
of the CEOS Working Group on Data, through the Catalog Subgroup,
to foster the exchange of information among international agencies.
The first release of the IDN was named the Prototype International
Directory (PID) in 1990. [Actual DIF exchange procedures were agreed
on by February 1991.]
In 1990, the Interagency Working Group on Data Management for
Global Change (IWGDMGC) adopted the directory as a prototype to
facilitate global change research - in response to the challenge
by the Earth System Science Committee (ESSC). Thereafter, the NMD
was renamed the Global Change Master Directory (GCMD) for its Earth
The DIF has enjoyed over 20 years of success. The DIF structure
has been flexible enough to evolve with growing metadata requirements,
especially for the geospatial disciplines. In the U.S., the Office
of Management and Budget's (OMB's) Circular A-16 for the improved
coordination of spatial data among federal agencies led to the establishment
of the Federal Geographic Data Committee (FGDC) and the FGDC Clearinghouse.
The GCMD serves as NASA's FGDC Clearinghouse node for geospatial
metadata. Elements of the Content Standard for Digital Geospatial
Metadata (CSDGM) were incorporated in the DIF in 1994.
In the late 1990s, the geospatial community began work towards
the development of an international standard for geospatial metadata.
The International Organisation for Standardisation (ISO) Technical
Committee's [(TC)211] Metadata Standard 19115 (previously known
as 15046-15) (see: http://www.isotc211.org/) sought to provide "a
consistent suite of geographic information schemata that allows
geographic information to be integrated with information technology.
The goal of this work item is to produce a schema for geographic
The ISO 19115/TC211 geospatial metadata standard was adopted June
2004. Required elements and appropriate modifications were approved
by the CEOS IDN Interoperability group and incorporated into the
DIF to achieve full ISO compatibility.
The DIF does not compete with other metadata standards. It is simply
the "container" for the metadata elements that are maintained
in the IDN database, where validation for mandatory fields, keywords,
personnel, etc. takes place.
The DIF is used to create directory entries which describe a group
of data. A DIF consists of a collection of fields which detail specific
information about the data. Eight fields are required in the DIF;
the others expand upon and clarify the information. Some of the
fields are text fields, others require the use of controlled keywords
(sometimes known as "valids").
The DIF allows users of data to understand the contents of a data
set and contains those fields which are necessary for users to
decide whether a particular data set would be useful for their needs.
The DIFGuide document provides information
about each field of the DIF, including its syntax, specifications,
recommendations, and examples. Several example DIFs are also provided.