Utypes 0.4 comments

[Norman Gray]

Mireille, hello.

On 2009 Nov 25, at 14:29, Norman Gray wrote:

> Here are some comments on v0.4 of the utypes draft at <http://www.ivoa.net/cgi-bin/twiki/bin/view/IVOA/Utypes>.

And the other thing I meant to mention, but forgot in the last message, is that we should think briefly about how utypes would appear within FITS files.  Whether or not we expect utypes to be often used within FITS files, it would be prudent to bear in mind that some file formats are more restrictive than XML about what can appear.

For example, we might imagine utypes appearing in a FITS file like:

PFX01SSA= http://www.ivoa.net/...
PFX02STC= http://www.ivoa.net/...
UTYPE001= ssa:blah
...

(see also Jonathan's suggestions in <http://www.ivoa.net/forum/dm/0610/1257.htm>).  But something like that would impose length limits on the sizes of prefixes and utypes as a whole: 'ssa:blah' could be at most 72 characters.

I've taken a very quick look at the EXIF and TIFF formats.  That doesn't look like it would impose length restrictions, but ... doesn't look like fun otherwise!

All the best,

Norman


-- 
Norman Gray  :  http://nxg.me.uk