TAP VOSI Information

[Doug Tody]

Hi Tom -

On Mon, 23 Nov 2009, Tom McGlynn wrote:
> I hadn't forgotten multi-position...  At least in the current PQL draft, the 
> only place you can use uploaded tables is in the multi-position query.  So 
> the service would specify that they supported multi-position queries by 
> giving the kinds of tables that a user can upload in PQL.   A service which 
> did not support multi-position queries would specify no supported sources for 
> table uploads in PQL.

I think this is too subtle, and would break anyway once we find
another use for an uploaded table. (One such case is querying the
uploaded table as if it were a data table - while not scientifically
useful, this could be very useful as a round-trip test for example,
since we know every detail of the input table.  So in this case we
have FROM=<upload-table> and WHERE=<whatever>.)

We may be approaching this wrong in any case.  Table uploads and
VOSpace support are capabilities of the main TAP engine, not the
query language.  To a query they are just another DBMS table.  So it
is probably better to just say whether the TAP service supports these
various cases of tables, and separately say whether PQL suppports
the multi-position query capability.

> I had overlooked one of the most critical options though, the supported 
> Formats.  Presumably the conventions adopted for the other DAL protocols can 
> be used here.

Good point.

> I'm not sure that row limits alone are enough.  The database may have BLOBs 
> or CLOBs which could be very large. Currently we tend to store metadata in 
> the database and data in the file system, but with modern database systems, 
> storing the data in the database could make a lot of sense. If a user has a 
> 500 MB data file in each row, just a few rows might be pretty nasty for a 
> download.

Ok, good point.

> I like your suggestion with regard to providing an indicator for the 
> underlying database.  In addition to being useful, it would be fascinating 
> just to see what choices our colleagues make.

Even if SQL pass-through is not supported it would be quite interesting
to know what back-ends are being used.

 	- Doug