NAME or ID

[Clive Page]

On Thu, 12 Jun 2003, Roy Williams wrote:

> The NAME is about readability, and should be used where humans see are to
> read. The ID is about uniqueness, so that computers can distinguish one
> column from another.
>
> If only NAMES are present, then these can be used in place of ID -- but only
> if uniqueness checking is done. If only IDs are present, these may be used
> as NAMES, but they may be meaningless (eg ID="F784673638")

Roy (et al)

Thanks for that clarification.  In that case I think that the VOTable spec
v1 is somewhat deficient, and we are already seeing the results of the
omission in incompatibilities of some files with some software.  A file
format specification with options really needs to specify to those who are
producing software that writes VOTable files what is essential and what
merely optional, so that those writing software to read VOTable can handle
all the possibilities.  I don't think it does that properly at present.
We can learn something here from the time it took the FITS spec to get
even roughly adequate.

There are a number of solutions I'd like to propose, e.g.

(a) Make both NAME and ID mandatory on file writing.  This simplifies the
task of reading, but some writing programs will be a bit more complicated,
e.g. converting from FITS where a valid table can have duplicate column
names, or none at all (so IDs have to be made up, e.g. "COL123")

(b) Make ID mandatory (with uniqueness tests on writing), and require
readers to default NAME to ID.

(c) Make NAME mandatory, and require readers to default ID to NAME (with
appropriate uniqueness tests, or alterations when non-unique names found).

(d) Require one or other (and allow both), with readers finding only one
of them defauting to the other (with appropriate uniqueness...).

I'd prefer (a), since a file may be read many times, but is usually only
written once, so this is more efficient overall.  But others may have a
different perspective.

Regards

-- 
Clive Page,
Dept of Physics & Astronomy,
University of Leicester,    Tel +44 116 252 3551
Leicester, LE1 7RH,  U.K.   Fax +44 116 252 3311