[TAP] data type for column metadata

[Patrick Dowler]

On 2009-03-24 11:06:17 Rob Seaman wrote:
> Try replacing the notion of a generic timestamp with "I am a distance"  
> or "I am a magnitude".  Is there really any useful reason for  
> expressing something so general purpose as "I am a timestamp"?  This  
> is very different from an epoch embedded in a data model such as "I am  
> mid-exposure".  If there is no specific data model, it isn't clear  
> that a utype has any utility.

One thing to remember is that TAP is a lower-level protocol in the sense that 
there may or may not be a (standard) data model describing the content. That 
means that there may well be a column with a timestamp in it but no 
applicable utype at all. The service still needs to be able to tell the users 
that column X has a timestamp so they can write correct queries. The rest of 
the meaning, as far as TAP is concerned, is not rigorously specified. 

So yeah, I agree: utype does not do anything in the general TAP case, sans 
data model. Further, the use of utype (in the metadata and in the output 
VOTable) should be left for services that combine the TAP protocol with a 
specific data model, so I would argue that TAP should not specify any use of 
utype at all. 

PS-you still have to know the datatype to write a syntactically correct 
query :-)
-- 

Patrick Dowler
Tel/Tél: (250) 363-0044
Canadian Astronomy Data Centre
National Research Council Canada
5071 West Saanich Road
Victoria, BC V9E 2M7

Centre canadien de donnees astronomiques
Conseil national de recherches Canada
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Victoria (C.-B.) V9E 2M7