SSA/SDM: ucds and namespaces

[Doug Tody]

Hi Ulrike -

> trying to implement an SSA service I still have some questions
> concerning the contents of the votable which my service is supposed to
> return:
> In the SSA Data Model Summary in appendix D of SSAP V 1.02 I feel some
> ucds are missing:  e.g. Dataset.DataModel (might be "meta.version"?),
> Dataset.SpectralSI ("meta.unit;em.wl"?), Dataset.FluxSI"
> ("meta.unit;phot.flux"?). Any special reason for that?

There is no reason for not having these missing UCDs, it is just
that we haven't been able yet to get all the people involved to
agree to them.  If you would like to propose values for some of the
missing UCDs we can try to get them in V1.1.  In most cases we will
need these added in the Spectrum DM as well.

> In the section "Protocol" of the summary table (on first page) there are
> two namespaces defined for SSA and spectrum data model. Does this mean
> the  utypes in the queryResponse and metadataResponse must have exactly
> these prefixes? Or can I use any prefix, just make sure it defines the
> SSAP namespace rsp. the Spectrum Data Model namespace?

In principle you can use any namespace prefix, however I would suggest
using the ones specified.

> Where do I need the Spectrum Data Model namespace? Up to now I only used
> SSA - utypes. I still do not see the difference. To me it looks like the
> SSAP  subsumes the  spectrum data model. (I admit, I haven't studied it
> thouroughly.)

The Spectrum DM namespace is only used in spectral datasets (e.g., a
spectrum returned in VOTable format).  The SSA and Spectrum data models
are the same, except that each defines some stuff which is not in the
other, and some things such as allowable units or defaults may vary.

	- Doug