On May 10, 2005, at 14:06, Jonathan McDowell wrote:
>
> The key phrase here is "requires a lot of extra parameters". In some
> other practical cases, a full description *is* required: so you need
> the
> parameters and a data model to relate them to each other. But if the
> data model is very generic you still need the UCDs to describe
> precisely
> what the individual parameters are.
>
> This is of course fuzzy, since sometimes - as in parts of STC - the
> utype implies what the UCD must be. But sometimes the utype describes
> only the precise relationship between two concepts, and the UCDs
> describe the precise identity of the concepts - both precise, but
> doing different jobs. Thus you might use utypes to
> link a velocity and its standard of rest, but you still need to
> use UCDs to explain that this is the escape velocity from the
> star (src.veloc.escape) and not the expansion velocity of the
> wind (src.veloc.expansion) that you're talking about.
> [...]
> Group 2
> - the velocity of what? (distinguishing different physics concepts):
> src.veloc.dispersion
> src.veloc.escape
> src.veloc.expansion
> src.veloc.microTurb
> src.veloc.pulsat
> src.veloc.rotat
>
Devil's advocate point of view
It looks to me as if you are trying to model a generic astronomical
source
by using UCDs. Wouldn't that be the role of a "Generic Astronomical
Source Data Model"
instead?
That is, the UCD could be src.veloc leaving to the utype of the GAS-DM
to tell which part of the source is being described.
Drawing a line between UCDs and UTYPEs is something we have not achieved yet.
The fact is that we have never really tried. I have never seen a VOTABLE using both UCDs and UTYPEs; until we see one and we experiment with it I fear we could philosophically talk about it for ages. We need real examples (self-criticism: hence we need some DM :-) ).
In my view, precise UCDs means: a pragmatic, though incomplete,
approach;
an approach that is useful to fill a gap: the absence of a DM.
To counter-balance such sentence I can certainly add that on the other hand, we will never have all the DMs we would need.
Help!
:-)
Alberto Received on 2005-05-10Z12:59:53