NOST News

CCSDS/ISO International Workshop

The Consultative Committee for Space Data Systems (CCSDS) held an international workshop in Frascati, Italy, from October 24 through November 4, 1997. This article reports on the major results listed below under "Archive Reference Model," "Data Entity Dictionary," and "Five Year Review of Standards."

Archive Reference Model (OAIS)

Approximately three days of the Panel 2 workshop were devoted to the archival work package with a major concentration on the "Reference Model for Open Archival Information Systems (OAIS)." The reference model in draft form is already getting significant publicity and favorable responses as reported by several participants. In particular, a United Kingdom workshop, organized by the British National Space Centre, was held to expose this work to a wider audience, and there was significant interest from those concerned about preserving the cultural heritage. A presentation on the model was also given to the Society of American Archivists annual meeting, in September 1997, and many favorable comments were received.

The Panel 2 workshop found that Version 2.0 was much improved. Key issues raised included the following:

• Review the use of "Access" and "Dissemination" to see if better terms can be found.
• Address the creation of new metadata, which is not a part of the original ingest process, that is used to improve descriptions of existing archival information packages.
• Relate the migration options to typical scenarios and add examples.
• Improve the Archive Classification section or delete it.
• Incorporate the Federation section into the main body of the document.
• Complete the illustrative scenario and remove excessive redundancy.
• Fill out the annex showing the relations of the reference model to other standards and models.

The document is still on track to become a CCSDS Red Book and an ISO Draft International Standard (DIS) in spring 1998. Participation in this work is encouraged, whether it is providing occasional comments or attending periodic U.S. and international workshops. To participate, please use the registration form accessible from http://bolero.gsfc.nasa.gov/nost/isoas/us/overview.html

Comments on this work are always encouraged. Please contact NOST at the NOST office.

NOST
GSFC
Code 633.2
Greenbelt, Maryland 20771

Data Entity Dictionary

• ISO/IEC 11179-3:1994 Part 3: Basic Attributes of Data Elements.
• ISO/IEC 11179-4:1995 Part 4: Rules and Guidelines for the Formulation of Data Definitions.
• ISO/IEC 11179-5:1995 Part 5: Naming and Identification Principles for Data Elements.
• ISO/IEC 11179-6:1997 Part 6: Registration of Data Elements.

Both these standards have been developing for a number of years along parallel paths. Recently, individuals involved in both the DEDSL and the ISO/IEC 11179 efforts participated in a Joint Metadata Registries Conference and shared their results. There was recognition that although both standards addressed similar areas, there were a number of important differences in the scope and detail of the standards. Although it did not seem practical at the time to merge these into a single standard, NOST felt that it would be worthwhile to harmonize the content of the standards. This harmonization could benefit users by allowing implemented systems to be conformant with both standards, and developed software would have a broader market.

As mentioned, DEDSL contained the same concepts and many of the attributes described in ISO/IEC 11179-3. However, DEDSL went beyond strictly identifying the concepts and specified the actual syntax used to express and exchange those attributes. The NASA team felt that users would be best served if CCSDS could alter the terminology used in the DEDSL specification to harmonize it with that terminology already present in ISO/IEC 11179. ISO/IEC 11179 also contained an easier, though perhaps less complete, method of specifying allowable values. NOST will likely adapt the ISO/IEC 11179 method since the current ASN.1 specification in the DEDSL specification is thought to be too complex to suit many end-users. Although many of the attributes in DEDSL were the same as ones in ISO/IEC 11179, others will require a little more tuning to make them consistent, and still others appear in only one of the standards. NOST will investigate the possibility of incorporating the attributes not previously included in the DEDSL set, thereby making DEDSL a superset of the ISO/IEC 11179 attributes.

Harmonization should work out well since there were plans to extend DEDSL to include attributes to express concepts such as relationships between objects that already exist in ISO/IEC 11179. Unfortunately, some of the concepts are not rigorously defined, and some additional work is required to incorporate those elements unambiguously into DEDSL. Since DEDSL also specifies the implementation of the concepts in a specification language based on the Parameter Value Language (PVL), NOST will also need to complete these extensions. Work is expected to progress rapidly with NASA providing input and the French Space Agency, CNES, working as editor for a new version of DEDSL. Hopefully, the new draft version will be out in the middle of 1998.

Five-Year Review of Standards

For PVL NOST will suggest the following:

• A few editorial/typographical errors in the original be corrected.
• It be made clear that all statements within a PVL module are ordered.

For SFDU-Structures some suggested extensions include the following:

• Adding additional SFDU classes, such as a Software Class and a Processing Class.
• Incorporating the Referencing Environment Standard into this one.
• Adding additional referencing techniques such as URLs.
• Extending a concept to handle multiple logical volumes.
• Standardizing the Volume Descriptor.
• Adding compound and complex relationships.
• Adding index structures.

E-Mail: nost@nssdca.gsfc.nasa.gov
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