SSA UTYPES

[Alberto Micol]

On Dec 19, 2006, at 19:07, Doug Tody wrote:

> The motivation for this is that we would like to use most of the
> same metadata for other DAL interfaces (at this level very little is
> specific to spectra),

Yes, though I would distinguish between the current phase (SSA V1)
and a subsequent phase (let's call it V2 for the sake of a name).

If I get the picture right, the main goal of V2 should be
to unify SSA and SIA by using a common underneath data model
(probably the characterisation dm), allowing thus common metadata
to describe n-dimensional data, being them spectra, images, data  
cubes, etc.

In V1 if I'm not wrong, the agreement is that SSA is based on the  
Spectrum DM 1.0.
The idea being to reach fast SSA1.0, leaving to the next version the  
role
of unifying things.

Basically I see V1 and V2 as well defined and intrinsically different.

Instead, reading SSA0.97 I get the impression that SSA1.0 will
be somewhere in between V1 and V2; and there is where my difficulty
originates. To state it clearly I think that SSA1.0 should
use Spectrum DM 1.0 as is (where possible of course), and not
deviate from it, as instead proposed in that 3.3.6 paragraph,
or as alluded in the Appendix 1 "Mixed Service".

> plus at this level we prefer to have the UTYPEs
> rooted in each component data model.  Hence, a UTYPE is something like
> "ssa:Target.Name".

So, the answer to my question was that it is an ssa name space then?!

Thanks,

Alberto

> As for SSA needing its own data model and namespace, probably it does
> anyway, as at level of the protocol additional metadata needs to be
> defined which is not relevant for Spectrum.  But the intention is
> that most of the metadata in SSA and Spectrum shares a common model.
>
> I like to make a distinction between a data model as an  
> abstraction, and
> an application of a data model in some context.  Two different  
> applications
> can share the same data model, without necessarily sharing  
> something in
> the implementation such as an XML schema.
>
>
>> To recap, depending on whether if I follow :
>>
>> 1. the statement in SSA 3.3.6,
>> 2. the SSA Appendix,
>> 3. the SDM v1 rel cand 1 rev 2
>>
>> I can come up with three (or maybe four) different utypes for
>> the same field:
> 	[...]
>> Could you please clarify?
>>
>> Thanks,
>>
>> Alberto
>> PS: BTW, I support Randy's comments that the examples given in the  
>> Appendixes
>> are really important to the developers. It would be so nice to  
>> have them
>> fully thought through, so to act as approved references that one  
>> could use
>> and adapt to his/her case... It would speed up development!
>
> As noted earlier, we merely haven't updated the Appendix yet.
> The UTYPEs will be as stated in the earlier sections of the document.
>
> I strongly agree that an example VOTable such as this (once updated)
> is an important part of the specification.  We are working on some
> actual SSA implementations already (also a Java toolkit which will
> deal with most of this!), which will also help to clarify all this.
>
> 	- Doug