[OBSERVATION]Observation data model/comments/Resolution...

[Martin Hill]

Hi Mireille,

Mireille Louys wrote:

>>>    2) If Resolution and Precision really might 'belong to' many different
>>>Characterisations, we need to make sure they are immutable.
> 
> what is this ? a kind of constant value? sorry , not clear to me .

Yes - sorry about the jargon.  It basically means a class that cannot be 
changed once constructed.  It's useful for complex classes that have a 
lot of inter-related properties, so that you can't change one bit that 
makes the whole thing invalid.  (For example, if you have an object 
representing '12 degrees', it doesn't make sense to allow the units to 
be changed to radians without changing the value too - either the object 
was wrong beforehand or it will be afterwards).

It's also useful (in this case) when you might have several references 
to the same instance, as seemed to be the case in this diagram.  In that 
case, we don't want one Characterisation changing a property in its 
Resolution if it's going to change a property in another Characterisation.

> 
> 
>>On the other
>>
>>>hand, we could say one Resolution/Precision instance can only belong to one
>>>Characterisation which might be neater and seems more correct somehow -
>>>presumably Characteristics normally have different resolutions?
> 
> 
> It is the case I think, for images at least . The Observed image have
> Characterisation descriptors , among them
> a Resolution component, a SamplePrecision component that are determined by:
> the instrumental chain and the data reduction pipeline.
> If a new reduction algo is developped, a new Observation will be produced with
> updated values for Characterisation compents.
> For a spectrum, this is probably the same situation.
> For a list of extracted sources , we have to check.

We probably ought to change the association link then so that a 
Resolution and a Precision only belong to one Characterisation.

>>>    3) Is ObservingConfiguration itself the ObsEltList?  What benefits do we
>>>get from having a separate List?
> 
> I can hook another Object: "Ambient conditions " for example under
> ObservingConfiguration,
> that can describe the instrumental parameters values for this  Observation shot.
> There could be more informations to store than just the list of elements.

Understood.

Thanks!

Martin

-- 
Martin Hill
www.mchill.net
07901 55 24 66