UCD problem in SSA/SpectrumDM

[Douglas Tody]

Hi Keith -

If we are going to be having a minor update of these documents there
are probably some other things which should go in as well that people
have brought up during the initial implementations and which we have
been saving for the next version.  The fix that Alberto mentions is
simple enough but we should be careful about broader data model changes
(e.g. to re-align the data model with the more recent version of Char)
as these will affect existing implementations.  If the changes are
significant we might better defer them to a 2.0 version.  In some
cases Spectrum did things slightly different than Char (e.g. the
detailed usage of STC I think) for what may still be valid reasons.
I don't think we should rule out possible minor changes to Char as
well, since after all both are RECs.

What is the policy for minor document updates?  Can we just put out
a 1.0x for a published recommendation?

 	- Doug


On Fri, 20 Nov 2009, Keith Noddle wrote:

> Hi Alberto,
>
> Following Bruno's recent evaluation of the SSA document highlighting among 
> other things a disconnect between the spectrum data model defined in SSA and 
> that of the Data Model WG, Mireille and I plan to review SSA and see what can 
> be done to reconcile this and other issues. We will obviously include your 
> observations below in such an exercise!
>
> Keith.
>
>> 
>> Dear DAL chair,
>> 
>> I'd like to mention a little but annoying problem with
>> the instrument bandpass as defined in:
>> 
>> - Spectrum DM
>> - SSA v1.04
>> - ssap-keywords.xls
>> 
>> (see below all references in those documents to the instr.bandpass UCD)
>> 
>> 
>> The problem is that the the wrong UCD is assigned to the central wavelength 
>> of the bandpass.
>> 
>> All documents mention the UCD "instr.bandpass" for the field identified by 
>> utype:
>> Char.SpectralAxis.Coverage.Location.Value
>> 
>> This is wrong because the central wavelength of a bandpass is a wavelength, 
>> not a bandpass.
>> The correct UCD should therefore be:
>> 
>> em.wl.central;instr.bandpass
>> 
>> 
>> and not just instr.bandpass.
>> 
>> 
>> How easy would be to ammend the SSA document with such an easy change?
>> 
>> 
>> (Without going into too many details, the fact that instr.bandpass is 
>> instead used
>> for a numeric field (central wavelength) makes the SSA validator fail the 
>> test
>> for the ESO SSA service, but that is a different issue that I will address 
>> within
>> a different forum. The problem here is that a wrong UCD is used.).
>> 
>> Many thanks,
>> 
>> Alberto
>> 
>> PS: All references to instr.bandpass in the mentioned documents:
>> 
>> 
>> Appendix D: SSA Data Model Summary:
>> -----------------------------------
>> 
>> DataID.Bandpass | instr.bandpass | Band as in RSM Coverage.Spectral | char 
>> | * |
>> Char.SpectralAxis.Coverage.Location.Value  |  instr.bandpass |  Spectral 
>> coord value |  double *** wrong UCD
>> Char.SpectralAxis.Coverage.Bounds.Extent   | instr.bandwidth   | Width of 
>> spectrum |  double
>> 
>> IVOA Spectral Data Model:
>> -------------------------
>> 
>> Spectrum.DataID.Bandpass | instr.bandpass | Band, consistent with RSM 
>> Coverage.Spectral | OPT | UNKNOWN |
>> Spectrum.Char.SpectralAxis.Coverage.Location.Value | instr.bandpass | 
>> Spectral coord value | MAN |     <PARAM ID="SpectralLocation" 
>> datatype="double" name="SpectralLocation" ucd="instr.bandpass" 
>> utype="spec:Spectrum.Char.SpectralAxis.Coverage.Location.Value"
>>  value="6515.408759029946">
>> 
>> 
>> 
>> ssap-keywords.xls spreadsheet:
>> ------------------------------
>> 
>> Bandpass         Spectrum.DataID.Bandpass  instr.bandpass  Band as in RSM 
>> Coverage.Spectral   SPECBAND  char * q                   SpectralLocation 
>> Spectrum.Char.SpectralAxis.Coverage.Location.Value  instr.bandpass 
>> Spectral coord value    SPEC_VAL        double           m    q
>> 
>> 
>
>
>
> -- 
> Keith Noddle                    Phone:  +44 (0)116 223 1894
> AstroGrid Project manager       Fax:    +44 (0)116 252 3311
> Dept of Physics & Astronomy     Mobile: +44 (0)7721 926 461
> University of Leicester         Skype:  keithnoddle
> Leicester                       Email:  ktn at star.le.ac.uk
> LE1 7RH, UK                     Web:    http://www.astrogrid.org
>