UCDs and arrays

[Baptiste Cecconi]

I tend to say that stat.distribution would be a better option than stat.probability or stat.likelihood. 

Markus, please send a request to the UCD working group, as described here: http://wiki.ivoa.net/twiki/bin/view/IVOA/IvoaSemantics#UCD_list_update <http://wiki.ivoa.net/twiki/bin/view/IVOA/IvoaSemantics#UCD_list_update>
(it will be good opportunity to check the process… :-)

Baptiste


> Le 7 mai 2018 à 10:17, Frederic V. Hessman <hessman at astro.physik.uni-goettingen.de> a écrit :
> 
> In a pinch one could use stat.likelihood (stat.distribution would be sort of the same), especially since one already has stat.probability (which I would use over stat.likelihood for simple single probabilities), but a stat.distribution would be a much cleaner solution.
> 
> Rick
> 
>> On 4 May 2018, at 19:40, Markus Demleitner <msdemlei at ari.uni-heidelberg.de> wrote:
>> 
>> Dear Semantics,
>> 
>> I'm having more and more array-valued columns in my TAP service.
>> Examples include:
>> 
>> * photometry points from Gaia DR2 (see the gaia.dr2epochflux table on
>> http://dc.g-vo.org/tap)
>> * the gavo_histogram aggregate function, again on http://dc.g-vo.org/tap 
>> (cf.  capabilities there), which computes, well, a histogram over a
>> column.
>> 
>> The question is: What should happen to the UCDs of such columns?  For
>> instance, in gaia.dr2epochflux, there are the columns rp_flux
>> (current UCD: phot.flux;em.opt.R -- yeah, we could quarrel whether
>> the R is a good choice here, but that's not my point now) and
>> rp_obs_time (current UCD: time.epoch).
>> 
>> I feel that's not quite right -- there's not *a* flux in rp_flux,
>> there's a *collection* of fluxes.  You could, of course, say that
>> clients can work out that it's a collection by inspecting the type,
>> and I'd not be disinclined to agree.  Does anyone disagree?  If you
>> disagree: What else should I put into the UCD attribute there?
>> 
>> The second case is, I think, even trickier.  Consider:
>> 
>> with sample as (
>>   select top 200000 * 
>>   from gaia.dr2light where parallax is not null) 
>> select gavo_histogram(round(parallax), 0, 200, 20) as hist
>> from sample
>> 
>> I guess I *should* have some UCD on the hist column ("this is a
>> distribution or parallaxes").  I don't right now (there's no UCD at
>> all).  pos.parallax certainly would be wrong.
>> 
>> However, there's already stat.min and stat.max (which are required
>> secondary, which makes perfect sense, since a minimal parallax
>> still is a parallax), and there's stat.error (which is required
>> primary, which again makes sense since the error on a parallax isn't
>> a parallax).
>> 
>> Now, I wonder: Could we have a stat.distribution (or something like
>> this) atom that would be mandatory primary (since a distribution of
>> parallaxes really can't be interpreted as a parallax)?  Would anyone
>> support such a proposal?  Would anyone object to it?
>> 
>>       -- Markus
>> 
>> 
>> 
> 

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