utype for STC region in SIAP query response

[Markus Demleitner]

Dear Colleagues,

On Thu, Sep 01, 2011 at 11:16:35AM +0200, Francois Bonnarel wrote:
> Hi Thomas,
>    To complete my answer to Markus
>     we could have something like
>        <FIELD name="fov" unit="deg" xtype="STC-s" datatype="char"
> arraysize="*" utype="sia:Char.SpatialAxis.Coverage.Support.Area" >
>           I think something like this can be proposed (if not yet the
> case) in SIA2...
>       this will be consistent with ObsTap... and could also be
> included in the next version of SSA et al.

Allow me to once again advertise the use of "standard" STC groups[1] --
while it's fine (and indeed necessary in many cases) for
protocol-specific data models have their own utypes for STC data,
multiprotocol clients greatly benefit if fields containing STC
information are marked up as such using the STC data model itself.
And the current problem -- identifying which field in a SIAP response
contains a region -- would be more or less solved just based on
existing IVOA standards.

So, I'd suggest to recommend including an STC group to SIAP responses
(which, actually, is already implicitely done by the VOTable spec).
For SIAP, this is pretty much boilerplate and looks like this for my
SIAP services (fix the refs as necessary for you, and you may need to
adapt the coverage's utype):

      <GROUP utype="stc:CatalogEntryLocation">
        <PARAM datatype="char" 
          utype="stc:AstroCoordSystem.SpaceFrame.CoordFlavor" 
          arraysize="*" value="SPHERICAL" name="CoordFlavor"/>
        <PARAM datatype="char" 
          utype="stc:AstroCoordSystem.SpaceFrame.CoordRefFrame" 
          arraysize="*" value="ICRS" name="CoordRefFrame"/>
        <PARAM datatype="char" 
          utype="stc:AstroCoordSystem.TimeFrame.TimeScale" 
          arraysize="*" value="TT" name="TimeScale"/>
        <PARAM datatype="char" utype="stc:DataModel.URI" arraysize="*" 
          value="http://www.ivoa.net/xml/STC/stc-v1.30.xsd" name="URI"/>
        <FIELDref utype="stc:AstroCoordArea.Polygon" ref="coverage"/>
        <FIELDref utype="stc:AstroCoordArea.SpectralInterval.HiLimit" 
          ref="bandpassHi"/>
        <FIELDref utype="stc:AstroCoordArea.SpectralInterval.LoLimit" 
          ref="bandpassLo"/>
        <FIELDref utype="stc:AstroCoords.Position2D.Value2.C1" 
          ref="centerAlpha"/>
        <FIELDref utype="stc:AstroCoords.Position2D.Value2.C2" 
          ref="centerDelta"/>
        <FIELDref utype="stc:AstroCoords.Spectral.Value" ref="bandpassRefval"/>
        <FIELDref utype="stc:AstroCoords.Time.TimeInstant" ref="dateObs"/>
      </GROUP>

To identify the column containing the region, you'd look for
(probably in this sequence, xpath syntax):

GROUP[@utype='stc:CatalogEntryLocation']/FIELDref[@utype="stc:AstroCoordArea.Polygon"]
GROUP[@utype='stc:CatalogEntryLocation']/FIELDref[@utype="stc:AstroCoordArea.Convex"]
GROUP[@utype='stc:CatalogEntryLocation']/FIELDref[@utype="stc:AstroCoordArea.Ellipse"]
GROUP[@utype='stc:CatalogEntryLocation']/FIELDref[@utype="stc:AstroCoordArea.Circle"]
GROUP[@utype='stc:CatalogEntryLocation']/FIELDref[@utype="stc:AstroCoordArea.Box"]

-- not too simple, but still preferable to having to know every data
model.

Moral: The rotten substitution groups in STC-X again mess things up
royally, and it would have been much nicer if STC-X had just defined,
say, Region and an attribute shape (or something), but it's too late
to cry over spilled milk now.  Since I can't see anybody moving to
review STC and its serializations, I'd plea to use what we have
rather than to invent new workarounds every time we encounter an
STC-related problem.

Cheers,

            Markus


[1] Ok, while the STC data model is a recommendation, the specific
form of the group is just a note,
http://www.ivoa.net/Documents/Notes/VOTableSTC/ (as is STC-X) -- but
the note hopefully reflects a wide consensus among the interested
parties.