WD for the Obscoredata model and its implementation on TAP

[Arnold Rots]

... WHERE em_min < X AND X < em_max AND em_unit = 'GHz'

Douglas Tody wrote:
> On Tue, 21 Dec 2010, Anita M. S. Richards wrote:
> 
> >
> >> Arnold - All of this is (except possibly adequate treatment of
> >> redshift) is already in the full model.  But ObsCore is a simplified
> >> subset intended only for data discovery.  Agreed something like
> >> reference position is needed for analysis, but that level of precision
> >> is not likely to be needed for data discovery.
> >> 
> >> Fixing the units is essential for discovery, at least if we plan to
> >> use TAP-ADQL expressions globally.  The primary requirement is that
> >
> > Why? Conversions are easy and don't even need trig !
> 
> Because 1) TAP-ADQL (SQL) is limited to simple arithmetic expressions
> for constraints on random table fields, and 2) we want to be able
> to send the same query to multiple ObsTAP services to do global data
> discovery.  So we will have something like (em_min < X AND X < em_max)
> to determine if X is within the spectral coverage of the dataset.
> Requirement 2) prevents us from doing unit conversion on the client
> side.
> 
> If instead PQL is used then we can support some simple frame/unit
> conversions directly in the service.  This would allow us to query a
> broader range of tables, not just ObsTAP tables (e.g. general catalogs
> or index tables).  But for ObsTAP we still need to fix the units to
> support ADQL queries.
> 
> On the other hand, if we give the user a nice application to do the
> discovery queries and display the query results then we can do the
> unit/frame conversions in the client application and make things just
> as the user wants.  In that case keeping the protocol simple, e.g.,
> by fixing units, makes the software simpler and more reliable.
> 
> (All a very old VO story of course...)
> 
>  	- Doug
> 
> 
> > all the best
> > a
> 
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Arnold H. Rots                                Chandra X-ray Science Center
Smithsonian Astrophysical Observatory                tel:  +1 617 496 7701
60 Garden Street, MS 67                              fax:  +1 617 495 7356
Cambridge, MA 02138                             arots at head.cfa.harvard.edu
USA                                     http://hea-www.harvard.edu/~arots/
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