[QUANTITY] Plea for pragmatism

[Alberto Micol]

Dear All,

At this point my feeling is that we are going nowhere.
All these discussions about quantities  are too phylosophical for me.

We need to focus on what we want to achieve, provided that it is clear
to everybody what the goal is. I might be wrong, but I do not think that
the goal is well identified within the group. (After all, this is why I 
called
for user cases).
I do not believe that defining a generic thing call quantity will bring us
anything immediately useful. It is too generic.

For example, sorry Brian, I do not understand the requirements in
http://nvo.gsfc.nasa.gov/cgi-bin/view_requirements.pl
Most of them in my opinion are not requirements, but definitions.

Requirements should describe what is to be achieved, and not
which class is associated with what, or who inherits from who.
And too generic requirements (quantity will be used to facilitate 
search, etc)
bring nowhere either.
 
In all cases, I do not find useful to start from the Quantity level.

Let's concentrate on the top level things we need to solve for the VO,
eg, how to describe coverage (bandpasses, regions, time intervals,  depths)
of existing data products, how to describe images, spectra, light curves,
exposure maps, visibilities, etc, how to package products, etc.

Those should be the starting points, because that is what we have to 
describe
in the 99% of the cases.

In the process of developing a data model to cope with these (already 
complex)
aspects, we will find the needs to define other things like Quantity, 
Phenomena,
or anything else that WILL RESULT USEFUL in the process. Not the other way
around!

I thought that it was decided that we start with Observational Data Model,
and not with Quantities. That is certainly a much more pragmatic point 
of view,
am I wrong ?

Alberto

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