Tom is right: and here is why this approach is wrong. (Was: Re: UTYPEs for SIAP)

[Brian Thomas]

On Thursday 01 April 2004 06:50 am, Tom McGlynn wrote:
> While I'm reluctant to get into this discussion -- I'm not sure
> that I can see any useful outcome in putting forward so
> divergent a view -- I feel this approach is just not right.
> Since I can't attend today's telecon, here are my thoughts after
> reading Jonathan's proposal.  Basically I don't see how it
> advances what we can do already.  I just need to look in a
> different field for a different set of strings to do the
> same operations that I'm doing today.
>
> Perhaps my problem can be traced back to my conception of what
> data models are for: they should provide a generic description of what
> can be done with a given data element.  If data models are so
> specific that they are directly tied directly to columns  of
> a table, then what is their utility?

	I find myself agreeing with Tom completely for the reason he supplies 
	(doesn't appear to advance present practice). I think *why* this is so, is 
	in large part related to the following:

        Many of the current problems with UCD1 (and UCD1+ and UCD2) arise because
        the current models are incapable of encompassing the real, complex, interrelated
        nature of these astrophysical concepts. Simple strings, plain and simple, just don't
        cut the mustard in this regard. Making patchwork, and incremental changes to 
        what are essentially broken models are not going to solve the problem.
	
	I have seen the UCD community move in the direction of creating hierarchical groupings
	of strings, (e.g. separation of fields within the UCD to give some groupings of the UCD's). 
	While this approach does provide a sort of interrelated hierarchy, all of the systems so far 
	restrict the  hierarchy of the concepts to being arranged within a pyramidal scheme (e.g. 
	groups within groups within groups.. up to the depth of nesting which the designer
	feels appropriate). Furthermore, all the concepts bear one-to-one relationships. I 
	belong to this group, therefore, as a concept, I am 100% part of that group. 

	Simply put, thats just not the reality of the astrophysical concepts. Many (if not most)
	concepts belong to more than one group, and when they belong to a group, their
	relationship may be qualified (ex. I belong to this group under the following conditions..)

	As a result, I don't see how pushing the strings as id's/concepts within UCD is going
	to be effective in the long run in terms of meeting VO requirements. We need to 
	take a more advanced approach, such as has been frequently suggested by UCD3.

	Why then, if we know that the current system is limited are we trying to make it go
	where it is going to be difficult to make it go? The effort is better placed on development
	of a better system, such as Quantity + UCD within an observation model rather than 
	tweeking present technologies including VOTable (not many may recall that one core 
	design principle for it was that it be a *simple* means to hold tabular data. It was never 
	intended to be a generalized data model) and UCD1 (ala UCD2).


	Regards,


	=b.t.