[utypes] Parsing utypes

[Mark Cresitello-Dittmar]

Markus/Omar,

I've been following along intermittently on the side.. but thought
I'd interject something here.

First:
   I tend to prefer declaring the namespaces used, mapping the namespace 
to some model.  For the SedLib code, I basically followed the thread 
Markus described.. pull out the declaration and find the namespace which 
maps to a the recognized model for Spectrum by the URI/URL (name.. not 
resolving the link).

   Defining fixed strings by model seems to make odd breaks.
   "spec" = Spectrum Model (1.*)
   "sdm"  = Spectral DM (2.*)
             - so all old Spectra need to change strings
             - but allows Photometry Point to share the same namespace
               without being too ugly.
    "ts"? = But when Time Series comes out (a similar extension of the
            base Spectral model as Photometry Point), it will presumably
            have it's own namespace because it is in a different model
            document.

But on to the point I want to make.

>> If The Things are universally defined they should be maintained somewhere.
>> You can't ask a new VO service developer to read all the IVOA documentation
>> just to get the list of reserved Things. Note that reading all the Data
>
> Ah, I'll need to chime in here -- the new VO service developer just has
> a list of strings (the structure of which she doesn't even need to
> understand) to embed in well-defined places.  Even the application
> developer doesn't need much more (she may need to parse utypes and
> juggle prefixes, though, if we go along with Omar's plans).
>
> The only people concerened with that global list of Things would be
> standards authors.  I think they can be bothered to read a few
> standards before they start writing one themselves...

Any data provider who wants to add non-modeled information (extend the 
model) needs to know the full set of allowed namespaces.

I'm not sure what mechanism is being defined for assigning Utypes for
extensions to a model, but the approach I keep hearing is that they
must be tagged with a different (provider specified namespace).

If I'm adding an item to the Curation object of Spectral DM:
   "sdm:Curation.Publisher"  <== modeled item
   "sdm:Curation.Date"       <== modeled item
   "bob:Curation.PubDate"    <== something I want to add.

In order to do that, they should be aware of the FULL set of reserved
namespaces in order to avoid accidentally using one.  Then there is the 
potential problem of IVOA coming out with a new namespace "bob" which
conflicts with the user-defined one?  They have a problem.

Mark