[Observation] draft observations

Hi all,

Comments on [Observation] v0.2:

Personally I'd like a little more in the Scope section about where Observation starts and stops, and where this particular document starts and stops. Eg, it will model the data used to describe an observation, rather than model the measurement's made from the observation (if I have it right!)

More generally, I think we need to be careful about using the term 'metadata' - one application's data is another application's metadata. Perhaps wherever metadata is used we should add 'of Xxxxx' so we know what data it's meta-ing....

Excellent diagram on p8 for non-techies like me; can it be placed near the table on p6? And/or a reference to it in the text at the beginning of 2.3 would make it easier to work through the prose.

I don't understand how the equation on p9 was built; what are the subscripts i and j? Are they just dimensions (position/time/energy, so we need more subscripts...) of some Photon measure x? Which ones are which and how does subscript j turn up in the equation when it's not in the prose? I take it it's trying to say that the number of photons measured with a particular characteristic (pos, time, energy) is dependent on the number arriving, the proportion of those detected and the proportion that are smeared to other values of the same characteristic. Is this enough? Don't things get smeared between axis for example (ie pos might smear in both spatial axis, high energy photons might cause smears in pos).

(p13, para 5) If Calibration is a Mapping that changes UCD/Units/Accuracy
then this could be difficult to implement under the current Quantity model. Is this a case for a QuantityMapping?

p13/14 bullets 1-3 - Can we leave modelling the Universe until later?! We need to model our data first :-) But seriously, this seems to be drifting into modelling object catalogues. I agree that object catalogues should be related to Observations, so that we can search/process based on object characteristics as well as observations, but can we model it separately?

(p14 sec 3) Is this just a way of saying that an Observation
might be made up of other Observations ('Composite' design pattern)? And we might want to add ObservationCube and ObservationSomething as particular types of Observation?

(p17) two different diagram languages and they don't quite seem to match up
:-) A few things:

1. I'd rather the ObsData illustration wasn't there - it starts introducing a different model to the wrong document. It works OK as a place holder.
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?

My apologies if some of this has been covered, I've had a run through my email box and didn't see anything like these.

Otherwise it makes sense to me as far as my astronomical knowledge goes, which is not all that far...

Cheers!

Martin

-- 
Martin Hill
Astrogrid/AVO, ROE
Tel: 07901 55 24 66