Empty TD element wording

[Doug Tody]

It would be good to make a distinction between a numerically indefinite
value (NaN for floating point) and no value (undefined, NIL, NULL,
etc.).  I think what is being talked about here is an "undefined"
value, i.e., an element for which no value has been assigned.  Even for
floating data, something other than NaN is needed to specify an
undefined value.  Since VOTable is a text format, the best way to do
this is probably with another magic string value of some sort, rather
than reserve a valid numeric value.  - Doug


On Tue, 20 Jun 2006, Mark Taylor wrote:

> I've had the following misleading wording in the VOTable specification
> pointed out to me.
>
> In section 4.6 it says:
>
>   In the TABLEDATA data representation, the default representation of
>   a ``null'' value is an empty column (i.e. <TD></TD>); for fields
>   containing arrays, individual ``null'' elements of the array can
>   be specified either by the value specified in the null attribute,
>   or by the "NaN" or "nan" text in place of the expected numeric value.
>
> This sentence only applies to certain datatypes; in particular it
> is not true of integer types (unsignedByte, short, int, long),
> which fact is made explicit in the relevant paragraphs of section 6.
>
> I suggest that (at such time as the next version of the VOTable document
> is released) the sentence above is withdrawn, or modified to make it
> clear that it applies only to certain datatypes.
>
> Mark
>
> -- 
> 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/
>