[TAP] data type for column metadata

[Markus Demleitner]

On Tue, Mar 31, 2009 at 02:19:27PM -0700, Patrick Dowler wrote:
> 
> I have been mulling things over and also talked with Arnold a bit, and this 
> was the result:
> [...]
> refsystem: reference system or scale
>  - values taken from STC, Table 2 (time), Table 3 (space), 
>  - values from FITS WCS Paper 3 Table 1 (energy): spectral CTYPE?
> refposition: reference position
>  - values taken from STC, Table 1
> flavor: what kind of a value is it? 
>  - could be taken from STC, section 4.4.1.2.2 (CARTESIAN, SPHERICAL, etc)
>  - could be taken from STC section 4.4.1.4.2 (for doppler/velocity)?
>  - includes differentiating JD vs MJD
>  - could be taken from FITS WCS style generally
[...]
> For many columns in a table, the values for refsystem, refposition, and flavor 
> will be null (not applicable), but for coordinate values they are necessary.
> 
> Comments on this? 
Risking I'm stomping on people's nerves: I'm not a big fan of coming
up with yet another incomplete representation of STC.  In addition,
this scheme, as far as I can see, doesn't tell you what's what in
multidimensional coordinates (ok, you could use the UCDs to figure
that out most of the time, but still), and which coordinate
pairs/triples belong together.

Again: What would be so bad with having clients request an empty VOTable
for the columns they are interested in to retrieve STC metadata?
While I haven't actually implemented it yet (but I'll do that RSN),
http://www.ivoa.net/Documents/latest/VOTableSTC.html sounds like a
reasonable representation of STC that people will need to implement
anyway (since they have to deliver VOTables, and in them getting this
kind of info as right as possible is IMHO even more important than
for TAP metadata).

Cheers,

          Markus