NOST News

Volume 13, Number 2, June 1997
By Donald Sawyer

This issue of the NASA/Science Office of Standards and Technology (NOST) News will provide highlights of the results from the recent Consultative Committee for Space Data Systems (CCSDS) Panel 2 workshop held in Silver Spring, Maryland, from May 11-20, 1997. The following topics were addressed:

Archiving Reference Model

Metadata Registration

Protocol for Accessing Distributed Catalogs

Data Entity Dictionary Specification Language

New Standards Approved: EAST and Referencing Environment

EAST Tools

All participation in these activities from government, industry, and academia is encouraged. Contact NOST for further information.

Archiving Reference Model

The archiving reference model effort (see http://bolero.gsfc.nasa.gov/nost/isoas/ ) is intended to provide a common set of terms and concepts that are useful in comparing and classifying archival systems handling digital data that may need long- term preservation. This will facilitate archive to archive communication and better support from vendors, and it will assist management in understanding archival requirements. The latest draft document, entitled "Reference Model for an Open Archival Information System (OAIS)," has been produced as a CCSDS White Book, Version 1, and it was extensively reviewed at the workshop. While there are a number of changes needed to improve the readability, including some reorganization, the document was found to be progressing well, and it was agreed that it could be widely circulated for comment. It is still on track for ISO Draft International Standard and CCSDS Red Book status in May of 1998.

An important benefit of the CCSDS program is the link it provides to the activities of other agencies and organizations. Some of the CCSDS participants from other agencies also participated recently in an initial meeting of the Committee on Earth Observing Satellites (CEOS) Archiving Task Team. The objectives of this effort are as follows:

CCSDS Panel 2 plans to work with CEOS to ensure that a full presentation of the reference model work is provided at their next meeting.

Metadata Registration

The utility of registering metadata, particularly in the form of descriptions of the format and meaning of data, has long been recognized by those participating in the CCSDS Panel 2 standards efforts and others. This utility allows the metadata to be managed and updated independently of the data that provides substantial efficiencies in the exchange and management of large volumes of data. A set of standards for the establishment and operation of distributed, largely autonomous offices that register metadata, called Control Authority (CA) offices, was achieved with the approval of the Control Authority Procedures and Control Authority Data Structures Recommendations in 1993 and 1994, respectively. These CCSDS/ISO standards have been used to establish a number of operating Control Authority offices, including one at the NSSDC.

European Space Agency (ESA) participants in CCSDS have made Web based software available to support the registration and dissemination of metadata by CA offices. This software is being upgraded to fix some deficiencies and to provide a socket interface for direct application access to registered descriptions. This will greatly facilitate the automated usage of the registered descriptions for such tasks as preparing well documented data packages for data exchange.

The essential element of ensuring global uniqueness of the identifiers assigned to any set of metadata starts with the coordination function played by a special CA office called the CA Agent. This entity keeps track of all other CA offices and the methods by which they may be contacted. The CA Agent is associated with World Data Center A for Rockets and Satellites, which is co-located at the NSSDC. Agreements were reached at the workshop that will enable the CA Agent to perform a "Domain Name Service" like function. The CA Agent will accept registered identifiers and return contact information for the CA office holding the metadata registered under that identifier. A prototype of this service has already been demonstrated.

These CA services map well into the current Internet draft on requirements for establishing a Universal Resource Name (URN) service, which is a big step beyond URLs in that links using URNs will be much less likely to break with the movement of data and machine addresses.

Protocol for Accessing Distributed Catalogs

There are many science disciplines that have an interest in accessing distributed data catalogs. The natural starting point for such efforts is to build on the Z39.50 protocol by developing one or more profiles.

The Earth observing community has been very active in taking this approach, and under CEOS they have devoted extensive efforts toward developing the Catalog Interoperability Protocol (CIP) based on Z39.50. They are also starting a prototyping activity for this protocol. CEOS has asked CCSDS Panel 2 to take on the task of turning this protocol into a recognized standard. The CIP includes many attributes that would be common across science disciplines, and it includes many attributes that may be unique to Earth observation. CCSDS Panel 2 would like to reorganize the document into a form that clearly separates the generic attributes from sets that may be specific to a discipline so that the other disciplines can take advantage of the extensive work already done. If this is to be accomplished, expressions of interest in this effort are needed. Interested readers who would like to find out more about this effort and possibly receive a distribution package planned for July 1997, please contact NOST.

Data Entity Dictionary Specification Language

Some of the NASA science disciplines have made good use of data dictionary concepts in formalizing the definitions of terms (data entities) so that more automated services can be provided. The efforts of the Planetary Data System are noteworthy in this regard. CCSDS Panel 2 has developed a language that may be used by disciplines and projects to carry this type of information in a standard manner. The intent is to promote the use of data entity dictionaries and to facilitate the interchange of such information among disciplines. The real problems in moving data from one standard format to another often are found to reside in uncertainties in the poorly documented meanings of the data entities.

CCSDS Panel 2 has developed the Data Entity Dictionary Specification Language, which includes both an "abstract" form and a concrete form expressed using the Parameter Value Language (ISO FDIS 14961). This draft standard was out for formal agency review for a period that ended in April 1997. However, the NASA review did not receive sufficient comments to provide a good basis for proceeding, so the review period has been extended until August 30, 1997. Readers with an interest in such work and who would like to make some comments, please contact NOST. A comment form and the current draft are available at http://ad05.atsc.allied.com/CCSDS_review/GRP9613.html.

New Standards Approved: EAST and Referencing Environment

The CCSDS Management Council has approved the EAST Recommendation and the Referencing Environment Recommendation as Blue Books, or new CCSDS standards. As described in the previous newsletter, the EAST specification addresses the problem of documenting data structures in a computer interpretable manner. The EAST Specification addresses problems such as the variety of operating systems or sensor environments generating a variety of data formats, the need for better understanding of the information by all users, and incomplete or ambiguous documentation.

The Referencing Environment specification defines "file pointer" mechanisms that can be embedded into other data structures including SFDU data structures. These "file pointer" mechanisms can be used when there is a need to link the internals of a file with other files (such as linking actual data records and the associated files providing information about the data records) when transferring such collections across computer systems or when storing them for future use.

EAST Tools

CCSDS participants from CNES, the French space agency, have been active in developing tools for using the EAST data description language.

The generation of EAST descriptions is supported by OASIS, which uses a graphical interface to assist users in describing the format of a particular record or file structure. OASIS Version 2.0, which runs on a Sun, will be available in July 1997.

The interpretation of EAST descriptions is handled by the EAST Interpreter. It parses the EAST descriptions and uses this information to parse one or more associated data files whose format conforms to the EAST description. The Interpreter, Version 2.0, which is written in C and runs on a Sun, will also be available in July 1997.

The ASCII_DUMP software uses the EAST Interpreter and displays the results as a table of data values. Version 2.0, which is written in C and runs on a Sun, will also be available in July 1997.

For more information on any of these activities, please contact NOST.

NOST
GSFC
Code 633.2
Greenbelt, MD 20771

E-Mail: nost@nssdca.gsfc.nasa.gov
Telephone: John Garrett, +1.301.286.3575
Telephone: Donald Sawyer, +1.301.286.2748
FAX: +1.301.286.1771

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Miranda Beall, beall@nssdca.gsfc.nasa.gov, (301) 286- 0162
Hughes STX, Code 633, NASA Goddard Space Flight Center
Greenbelt, MD 20771, U.S.A.

Erin D. Gardner, gardner@nssdca.gsfc.nasa.gov, (301) 286-0163
Hughes STX, Code 633, NASA Goddard Space Flight Center
Greenbelt, MD 20771, U.S.A.



NASA home page GSFC home page GSFC organizational page

Author:Miranda Beall
Curators: Erin Gardner and Miranda Beall
Responsible Official: Dr. Joseph H. King, Code 633
Last Revised: 26 June 1997 [EDG]