[QUANTITY] Plea for pragmatism

[DIDELON Pierre]

> From owner-dm at eso.org Wed Oct 29 12:59:05 2003
> Date: Wed, 29 Oct 2003 11:52:40 +0000 (GMT)
> From: David Berry <dsb at ast.man.ac.uk>
> To: Alberto Micol <Alberto.Micol at eso.org>
> cc: dm at ivoa.net
> Subject: Re: [QUANTITY] Plea for pragmatism
> 
> I tend to agree with Alberto that the requirements for the underlying data
> container model (be it called QUANTITY or something else) will probably
> become apparent as we consider further the higher level OBSERVATION model
> which we started to put together at Strasbourg.

OK. A general framework would be usefull to place in situation
the small part we are modelling meanwhile the "complete" DM is achieve.

Data containers ARE NOT restricted to QUANTITY, at least for some of us.
That a major point on which we have to agree before continuing modelling,
I agree it is part in a certain manner of high level modelling decision.
If we agree to separate these two domains, I think that we have made a great
step forward (hoping we are not just standing in front of a pit).
Can we try to achieve something very simple, like the simple quantity proposed
by Pat (off the list), before trying to use our skill and energy
on complex issues like "Universal Data Container".

> 
> Having said that, I think it would be useful to have a simple overview of
> what a candidate data container may look like, just so that we can check
> if it is able to meet the requirements which emerge as we develope the
> OBSERVATION model, and change it as needed. I'm thinking here of something
> as simple as the following:
> 

Once we have to tackle this subject, I think I would agree with most 
of the points below, except QUALITY, and add COVERAGE, COMPLETNESS (lacunarity)
at least.

> A Data Container (purposefully avoiding the potentially overloaded
> word "QUANTITY") has one mandatory component called "DATA" which
> contains (somehow - details to be decided) the actual data values. In
> addition, it can have any or all of the following optional components (all
> details to be decided):
> 
> ERROR - gives an estimate of the random error on each value in the DATA
> component.
> 
> QUALITY - gives a set of flags and/or enumerated values for each value in
> the DATA component.

This is a very complex information, very diffucult to attribute, which can
evolve with time, depend on the subject studied...
One data set unusable for a certain study, can be perfect (if not better) 
for another one.

> 
> LABEL - identifies the phenomenon measured by the DATA component (maybe a
> UCD?). Having a component to identify the contents like this avoids the
> need for a separate sub-classes for each of the potentially large number
> of phenomena which we may be interested in.
> 
> UNITS - identifies the units of the values in the DATA component
> 
> WCS - Contains a collection of world coordinate systems in which
> positions within the DATA component can be described, together with
> Mappings which describe how to transform positions between different world
> coordinate systems.
> 

Reference frame is more general and certainly more appropriate?

> TITLE - A descriptive title for human readers
> 
> 
> Obviously, there are many details missed out in the above, but I suggest
> this list as a target to be shot at as the OBSERVATION model is developed
> further. We made some good progress on OBSERVATION - whereas we seem to be
> getting bogged down on QUANTITY.
> 
etc...

but I think we must concentrate on the domain definition,
(the global view your asking for [OBSERVATIONS]) and we can at the same time
try to model a small well delimited concept to exchange (hopefully efficiently)
small amount of data (atomic value or small arrays).

Pierre
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DIDELON                               e-mail : pdidelon_at_cea.fr
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