Further thoughts on nulls in VOTables.

[Mark Taylor]

Readers of the dal mailing list may be interested to know that Tom's
comments are copied and are being discussed on a page on the wiki:

   http://www.ivoa.net/cgi-bin/twiki/bin/view/IVOA/VOTableIssues

I have CC'd this message to the votable list, which didn't get a copy
of the original message, as well.

Mark

On Thu, 21 Jul 2011, Tom McGlynn wrote:

> A brief discussion we had a few weeks ago with regard to nulls in VOTables and
> TAP noted the origins of the current conventions which I had been blissfully
> ignorant of.  I remain concerned that there are real issues that may arise as
> we try to support general table ingest and queries using VOTables for the
> serialization of the data.  The issues I see are:
> 
>    1. Real fields in VOTables cannot distinguish nulls and NaNs
>    2. The specification of nulls for strings and the mechanisms
> for distinguishing null strings and 0 length strings are unclear.
>    3. Integer columns may be required to confuse actual data and nulls
>    4. Robust serialization of query results involving integers and
> strings is incompatible with streaming results.
> 
> The attached document elaborates on these and I'd be interested in others'
> thoughts.
> 
> 	Regards,
> 	Tom McGlynn
> 

--
Mark Taylor   Astronomical Programmer   Physics, Bristol University, UK
m.b.taylor at bris.ac.uk +44-117-928-8776 http://www.star.bris.ac.uk/~mbt/