Format of concatenated UCD's

[Frederic V. "Rick" Hessman]

After withdrawing my suggestion of replacing the UCD ';' separator, we
went back to the drawing table.   One of our students came up with a
practicable solution: defining all UCD elements as a set of restricted
strings defined by a regexp.  The resulting (test) schema

	http://monet.uni-sw.gwdg.de/cgi-bin/xml_validation/scripts/ 
createUCDSchema.pl

why not elegant (in the sense that a set of <enumeration>s is elegant)
conforms exactly with the present usage, permitting lists of UCD groups
(separated by spaces), each with optional semi-colon separators.   This
example script takes the official UCD list and parses it into the  
correct form.
The parsing overhead is reasonable, especially since we're unlikely to
expand the UCD list to tens of thousands of entries any time soon.

I sense that there is some reluctance to have the UCDs parsed, though
I haven't yet heard any good reason for allowing garbage UCDs in
documents.

I'd like to see the use of parsed UCDs alongside what the VOEvent
group has been discussing as VOConcept (same syntax as UCDs,
different purpose) which would allow elements such as

	<Thing purpose="{list of UCDs and VOConcepts}"/>

e.g.

	<Explanation description="event.burst em.opt"/>

(dummy example for an optical burst) where you can see that the  
combination
of standard UCD syntax with VOConcept added is exactly what one needs  
to extend the present
functionality while keeping the same usage.

Yes, one can do this without syntax checking, but that's the whole
point of VOEvent - to permit strict syntax checking by computers using
standard elements.

Comments?

Rick

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Dr. Frederic V. Hessman      Hessman at Astro.physik.Uni-Goettingen.DE
Universitaets-Sternwarte     Tel.  +49-551-39-5052
Geismarlandstr. 11                Fax +49-551-39-5043
37083 Goettingen                 http://www.uni-sw.gwdg.de/~hessman
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