[OBSERVATION] Re: Observation data model comments

[Jonathan McDowell]

Martin

Thanks for your (Friday) comments on Observation.
I've tried to address your comments (and some of Anita's) in a v0.23
now on my site
 http://hea-www.harvard.edu/~jcm/vo/docs/obs23.pdf

A comment on the crucial equation that you discussed - I've
tried to clarify it in the text. Indeed your phrase
'smeared to other values of the same characteristic' is wrong,
the R function is indeed intended to smear across axes, and
the i and j indices label different characteristics. In the
equation I was using the `free index' convention beloved
of relativists; I have recast it as bold face vectors which I hope
is clearer; R = R(x1,x2,x3...,y1,y2,y3...) = R(x,y).

About modelling the universe later: yes, I mostly agree, but I think
we need to introduce these concepts now to clarify the
distinction between sources/objects and targets; the idea
of a target or a field is definitely within the realm
of Observation. Because many people mostly observe single astronomical
objects as their targets, they often mentally confuse the two
concepts.

I'd like to ask Mireille to comment on the following which I think
apply to her diagrams:

> 
>     2) If Resolution and Precision really might 'belong to' many different 
> Characterisations, we need to make sure they are immutable.  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?
>     3) Is ObservingConfiguration itself the ObsEltList?  What benefits do we 
> get from having a separate List?
> 

 - Jonathan