datatype values in TAP_SCHEMA.columns

[Patrick Dowler]

On 04/06/14 02:37 AM, Mark Taylor wrote:
 > A related issue is use of non-database type values (e.g. votable:long
 > in the above) in this column.  I think it's not legal (anyone disagree?),
 > but I've had a conversation with Pat about this in the past and I
 > think he has some reason for wanting them in there anyway.

The reason I did this is because I wanted to use array types in the 
tables and map them trivially to votable. This is used for the couple of 
columns in SIAv1 votables that have arraysize="2". It seemed that using 
datatype="adql:DOUBLE" size="2" in the tap schema was more likely to 
confuse clients than using datatype="votable:double"...

That votable-prefixed value comes from VODataService and can be directly 
used in valid VOSI-tables output. Since TAP_SCHEMA and VODataService 
descriptions were designed to be compatible, it seemed like a 
good/acceptable idea to use them.

  guess I have one other alternative: I could use datatype"adql:DOUBLE" 
and size="2" instead of that votable-prefix... would that be 
bad/unexpected for clients? It is valid VOTable but that column can only 
be selected and not used in the where clause (well, is [not] null would 
work) in ADQL.


And now we come full circle to my first response: this comes down to 
using TAP beyond the lowest-common-denominator mode. In this case I have 
non-standard datatypes (arrays) that I can get to work in the system 
with a little bit of flexibility. I think that should be OK and is a 
feature of VO standards that they can be used to go beyond the spec... I 
don't think TAP can say that no one can use arrays, or 
arbitrary-precision values, or URI, or UUID, or COLOUR, or any other 
datatype they might have in the DB and could encode in VOTable (with a 
suitable xtype aka tap schema datatype to warn people it is something 
custom).


my 2c,

Pat



-- 

Patrick Dowler
Canadian Astronomy Data Centre
National Research Council Canada
5071 West Saanich Road
Victoria, BC V9E 2E7

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