Indicate inter-dependencies amongst IVOA standards

Text to go in the 2008 Assessment and Roadmap document

Quite often an IVOA standard may depend on more other standards (eg a specific DM and STC), it would be useful to formally indicate this at least on the RFC page during the RFC period and in the document itself.

That discussion should be coordinated with the Standing Committee on Standards and Processes.

This point is particularly valid for the use of STC.

The STC system for astronomical coordinates and regions is an IVOA recommendation, and therefore we will all gain through interoperability. This interoperability is not just for technical systems, but also so that concepts learned in one area of VO can be applied in other areas. STC is applicable in many areas: ADQL, footprints, TAP, VOEvent, SIAP, source VOTables, etc. If a WG is intending to make a different representation of coordinate or region, they should explain why they are diverging from a standard already agreed. Further, the new representation should be simply and transparently convertable to STC to promote interoperability.
Identifying and using a single VO standard for space/time coordinates seems a foregone conclusion. The alternative would be chaotic, non-interoperating systems and software, which would confuse our users and annoy our sponsoring organizations. STC has been adopted as that standard - more to the point, no other option has been suggested. The sooner we begin to understand, use, and evolve STC (as appropriate), the better. This also ties in closely to the recent adoption of new IAU coordinate systems, see for example: http://www.adass.org:8080/Conferences/2007/Venue/people/participants/abstract?abstract_id=234. When the notion of sidereal time is no longer valid, clearly some new software framework is needed for coordinates. (RobSeaman)

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