Followup to Re: utype questions

[Doug Tody]

On Mon, 6 Jul 2009, Brian Thomas wrote:

> On Thursday 02 July 2009, you wrote:
>> The main point I think you are missing is that UTYPE is not a complete
>> stand-alone mechanism for modeling or storing complex data (nor is UCD,
>> VOTable, FITS, etc.).  It only addresses a portion of the problem.
>> So for example, there is nothing about UTYPE which is specific to
>> VOTable, or FITS, or a DBMS, or a Java class, or a param file, etc.,
>> hence we do not need to discuss all these applications in the UTYPE
>> specification.  Nor does UTYPE tell us how to model complex data.
> 
> I will assume you mean by that last sentence only key-value pairs
> and nothing more complex than that.

Complex data can still be modeled using UTYPE-based models, it is
just that it is done at a higher level by associating simpler models
(the simpler models have been parameterized or "flattened" using
UTYPEs).  Basically this is the relational approach vs an explicitly
hierarchical approach.  It works very well up to a certain level
of complexity, after which an explicitly hiearchical approach may
be justified.  But for most things simple property lists / keyword
tables / parameters etc. (they are all essentially the same concept),
or logical associations of these entities, will be adequate and will
provide a simple approach with maximum flexibility.  The model itself
can still be sophisticated, it is the representation and handling
within programming environments and languages which is simplified.

Regarding the draft spec we are still working on that so I won't try
to comment here on the details at this point.

 	- Doug