Utypes & VOTable

[Francois Ochsenbein]

Hi Jonathan,

Good starting point for a clarification of the utypes !
Remember, we also decided at the Beijing meeting to prepare a
note about the VOTable and STC connections shared by you,
Arnold and me -- a very first draft was posted last week (available 
as http://www.ivoa.net/internal/IVOA/IvoaVOTable/note_stc.html
or http://www.ivoa.net/internal/IVOA/IvoaVOTable/note_stc.pdf).
The note contains actual examples which could be interesting
for your purpose.

Just a few comments:

-- omitting the left-most parts of a utype (section 1.1): in the 
   VOTable/STC connection note I just mentioned, I've deliberately
   assumed that the full hierarchy is kept in the utype, even in the
   case of PARAMs defined within a GROUP having a utype. Should this
   be more extensively discussed in Cambridge ?

-- case-sensitiveness (end of section 1.1): the utype syntax has to
   follow the data model rules -- and if the components of a data model
   are case-sensitive, the utypes have logically to be case-sensitive, too.

-- utypes "a la UCD" (section 1.3): I share Doug and Pedro's opinions,
   I don't really see a necessity to add the semi-colon rule which makes
   the relation utype-data model more complex without obvious advantage.

-- unique instances of utypes in a VOTable (section 1.4): no, no !
   utypes and UFIs are different things -- and play different roles.
   Better not to mix them up.

-- value fields: if I correctly understand, the proposal just means that
   the default "unnamed" element is "Value", i.e. that
   <foo>12.3</foo> , <foo><value>12.3</value></foo> and <foo value="12.3"/>
   could have exactly the same "foo" utype. This makes sense, but I feel
   an explicit convention would better be specified, e.g. that any ".value"
   component should be removed in a utype.
  
See you soon,

Francois

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Francois Ochsenbein       ------       Observatoire Astronomique de Strasbourg
   11, rue de l'Universite F-67000 STRASBOURG       Phone: +33-(0)390 24 24 29
Email: francois at astro.u-strasbg.fr   (France)         Fax: +33-(0)390 24 24 17
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