Volume 16, Number 1, March 2000
By Donald Sawyer and John Garrett
The draft CCSDS/ISO standard "Reference Model for an Open Archival Information System (OAIS)" had been issued as a CCSDS Red Book for formal review within the space agencies. It was supposed to have been issued as an ISO Draft International Standard (DIS) at the same time, but because of ISO secretariat problems, the ISO review has been delayed. It should be underway by March 15, 2000, and will then run to about mid-August 2000. Consequently, the review period for CCSDS agency comments has been extended to be coterminous. Comments may be submitted by following the instructions at http://www.ccsds.org/RP9905/RP9905.html.
CCSDS Panel 2 is developing a specification for the formalization of attributes used to describe data elements. This specification facilitates the exchange of data entity dictionary information, whether it applies to a whole discipline or to a particular data product. This work has been harmonized with the data element description and registration standards being developed by ISO SC 32 and known as ISO 11179. Several federal agencies are active in developing and promoting ISO 11179 as a way to improve the reuse of data elements in their systems. Their standard is an abstract specification. The CCSDS "Data Entity Dictionary Specification Language (DEDSL)" is both an abstract standard and one or more concrete specifications. It also only requires a small subset of the possible attributes, while allowing users to create and document their own additional attributes. The DEDSL-abstract syntax was finalized at the workshop. The first concrete syntax, based on Parameter Value Language (PVL), is nearing completion and will be followed by an Extensible Markup Language (XML) based syntax. The first two documents should be available for formal review by early summer 2000.
Presentations and demonstrations using CCSDS/ISO standards were given by members of the participating space agencies. Highlights are as follows.
European Space Agency (ESA)/ European Space Research Institute (ESRIN) Archive Management System (AMS)
The ESRIN archive has developed the AMS to provide files of Earth science data to requesters. It uses the EAST Data Description Language (CCSDS 644.0-B-1) to provide an inventory mapping to blocks within a given file to provide a useful and automated subsetting capability. (http://www.ccsds.org/p2/presentations/ams2.ppt)
The National Space Science Data Center is migrating files from VMS-based optical platters to DLTs and raid disks. They are creating Archival Information Packages (AIPs) consisting of a data file in canonical form (a byte stream) together with an NSSDC standard attribute object written using PVL (ISO 14961:1997/CCSDS 641.0-B-1). The packaging uses Standard Formatted Data Units (ISO 12175:1994/CCSDS 620.0-B-2.1). The AIPs are stored on DLTs and the attribute objects and canonical files are then extracted and stored on the raid disk for rapid access.
Control Authority Agent
The National Space Science Data Center demonstrated a prototype "URN-like" service for access to data descriptions registered at various Control Authority offices among the space agencies. Entry of one of the unique identifiers originally assigned by some Control Authority office resulted in a query being sent to that office and the return of the data description.
The British National Space Centre (BNSC) representative demonstrated an XML-based prototype version of the Standard Formatted Data Unit packaging information, including the identification of the "class" of the object and the unique identifier assigned by a Control Authority. Efforts to combine this with JAVA-based classes triggered by the unique identifiers is also being investigated.
This international conference on metadata registries was held in Santa Fe, California, during January 2000. Its focus was on managing the semantics of data to be shared among systems and disseminated via the Web. The organizers were key developers of ISO 11179, a set of standards for describing and registering data elements. NASA contributed three papers. The first, by Louis Reich/CSC, compared CCSDS DEDSL with ISO 11179. The second, by John Garrett/RITSS, compared the CCSDS Control Authority standards with corresponding ISO 11179 standards. The third, by Steven Hughes/JPL, described the uses of XML/DTDs and the DEDSL standards to further describe profiles of distributed resources accessible via distributed queries over CORBA.
For further information on any of these topics, readers may contact Donald Sawyer .
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