C2MS13 — Create PSMs for at least XML and REST/JSON

In C2MS 1.0, XSDs were provided by NASA Goddard and published as 'normative' along with the spec. However, these were somewhat incomplete and not maintained by OMG, so these were removed as part of C2MS in 1.1.

The issue is that we do need to supply some PSMs to encourage C2MS usage in the space community, including the following:

• XML PSM (replace the GMSEC-supplied XSDs from 1.0 and the informal 1.2)
• REST/JSON PSM - to make it more modern and usable in modern architectures.
• Also consider PSM for Protobuf
• Others? IDL?

The intent should be to stop using NASA Goddard as the point of contact for all things C2MS. In fact, OMG should supply these PSMs to Goddard as input, rather than Goddard supplying XSDs to OMG as happened in 1.0.

Additionally, a REST/JSON and/or Protobuf PSM should focus on non-pub-sub usage... something that can exist and operate in a services-based architecture. In this case, it could be that the message subjects are ignored as these are used entirely for pub-sub subscriptions/delivery.

Related to the above, we COULD make subjects part of a PSM rather than PIM??? However, this probably isn't feesible in a 1.x baseline. We do discuss that these are optional, but it is also possible to use them for straight filtering, rather than just pub-sum.

Any PSM should consider including example messages based on the schemas provided by the PSMs.

PSMs can be done as new chapters within the spec, perhaps in a C2MS 1.3 release.

Note this text from C2MS13-3, which was originally created in 2018: "Due to lack of the ability to have multiple independent implementations of GMSEC due to its message-building API functions in source code, it would be appreciated if there were an XML PSM available. This would allow for an independent implementation apart from the single known implementation at this time. At this time, there is no known PSM that enables implementation of C2MS at this time that does not depend on FOSS or government-licensed IP."