utype questions

[Arnold Rots]

Norman,

You touch on one of the central issues that have made me very
uncomfortable with Utypes (but I assuem everyone is well aware that I
don't like them). See below.

  - Arnold

Norman Gray wrote:
> 
> Rob, hello.
> 
> On 2009 Jul 1, at 14:56, Rob Seaman wrote:
> 
> > Isn't the intended usage for utype something like:
> >
> > 	<whatisit utype="ns:target.class">whatitis</whatisit>
> >
> > When Doug says:
> >
> >> A major point of UTYPEs is to provide a simple, direct, and  
> >> *unique* way to specify the field of a specific data model.
> >
> > Isn't this in reference to the value of the utype attribute in the  
> > example above?
> 
> I think that here the utype ns:target.class is an item in a datamodel  
> (ontology of measurements) which indicates what role the <whatisit>  
> element is playing, and the value of this, the 'whatitis' is  
> potentially drawn from a _different_ ontology or vocabulary of  
> physical objects.  I agree that there's a potential issue about  
> legislating for this value, but believe that the lack of legislation  
> doesn't necessarily matter.
> 
> This is presuming that ns:target.class isn't one of those utypes that  
> only makes sense when it's coordinated with a set of other utypes from  
> the same model (the goal 1 of utypes, as I understand it).  If it  
> makes sense by itself, then that's excellent, it means that it's been  
> artfully repurposed here, and an application can reliably/safely  
> understand this bit of XML without necessarily having heard of the  
> <whatisit> element before.

This is the crux of the matter. A model never consists of a single
item. It is usually described by a set of information items (for lack
of a better term) that together convey the full meaning that the
author intends to convey.
The problem with Utypes is that it allows cherry picking of
information items with no guarantee that the information is complete,
or even makes sense. Consistency, completeness, and uniquenness have
been abandoned.

> 
> Best wishes,
> 
> Norman
> 
> 
> -- 
> Norman Gray  :  http://nxg.me.uk
> Dept Physics and Astronomy, University of Leicester, UK
> 
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Arnold H. Rots                                Chandra X-ray Science Center
Smithsonian Astrophysical Observatory                tel:  +1 617 496 7701
60 Garden Street, MS 67                              fax:  +1 617 495 7356
Cambridge, MA 02138                             arots at head.cfa.harvard.edu
USA                                     http://hea-www.harvard.edu/~arots/
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