[Moims-dai] MOIMS-DAI responses to MOSSG

David Giaretta david at giaretta.org
Wed Sep 14 14:34:14 UTC 2016

As discussed at the DAI webex yesterday, and with further exchanges of
emails, here is a collection of comments on the MOSSG paper.




1)      Although the paper states "Archive ingestion is not considered part
of the IOAG interoperability goals.", nevertheless as is recognised in
"However, the assumption is that there are mechanisms for archive ingestion
implemented", it will not be possible to get data out of an archive unless
data is ingested into it. MOIMS-DAI covers data ingest and should be
mentioned in the document, for example CCSDS 651.1-B-1, Producer-Archive
Interface Specification (PAIS). Blue Book. Issue 1. February 2014.

2)      The use of the word archive is misleading. What is discussed in most
of the document is what might be termed "short-term storage". For example,
the Service Description of the kind "Archive of Agency Y is accessed by
Agency X to.", which implies simple access to the bits which have been
stored. Interoperability normally means being able to use the bits. 

The MOIMS-DAI work on archives is about maintaining the usability of the

If agencies X and Y use the same format and semantics for the bits then
there is no problem. If one the other hand they do not then agency X will
need additional information. This may be relevant if there is a long time
between the creation of the data by Agency Y and the use by Agency X. It may
also be relevant if there is very little time between creation and use, for
example if the agencies use different systems. 

This is recognised in slide 29 in the PowerPoint presentation which has, at
the top level (with additions/changes marked in red):

Integration levels



of Interoperability

Ops, engineering and science teams from various space agencies  need to
integrate their data in an archive or a set of federated archives, and
update/retrieve from them, both during the mission lifetime, and in
long-term archives post-mission.  

Agreed common data formats (data standard), agreements on metadata content,
compliance with long-term digital preservation practices, such as CCSDS
standards for OAIS, PAIS and future protocol-level standards yet to be
developed by CCSDS.  




There are several problems with the original right hand side:

a)       Agreeing formats is not adequate. For example the agencies could
agree to use CSV - but what do the elements mean? what are the units? Is
agency X going to combine something measured in meters with something
measured in feet? In other words what metadata content is needed? This is
what DAI is concerned with.

b)      If Agency X wants the data from Agency Y after Y's project has
ended, can one be sure that the right metadata has been collected? MOIMS-DAI
checklist to help ensure that enough of the right kinds of metadata is
collected. Of course ensuring the data continues to be usable despite the
inevitable changes over time in software, systems, semantics etc., is
covered by CCSDS 650.0-M-2, Reference Model for an Open Archival Information
System (OAIS). Magenta Book. Issue 2. June 2012.



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