Revised ImageDM-ObsCore architecture

[Douglas Tody]

Hi Mark -

This second version looks like a step backward to me.  It seems clear
that ObservationDM is the basic general data model.  ObsCore is a
specialization of Observation defining a "core" subset of attributes,
plus (in its ObsTAP extension) it defines a specific, restricted mapping
to a table.  This was the case with your previous version, but this
latest one has ObsCore as the root data model which seems quite odd
since ObsCore is a subset of a more general model.  Actually I am not
sure there really is an "ObsCore" model at all; it seems that what we
really have is the ObservationDM with ObsCore/ObsTAP defining a specific
application (like ImageDM, SpectralDM) including a core/mandatory set of
fields and a specific table mapping.

Within Observation, naming the main class ObservationDataset seems
arbitrary to me.  Naming this class just "Dataset" would work as well.
To some extent the choice of name is arbtrary, but there is no reason
that we could not model an Observation separately from its use within a
Dataset.  There are use cases for example, where a single Observation
could result in several Dataset objects (e.g., a cube, a 2D image, and a
catalog all derived from the same Observation).  In fact, that is the
whole point of obs_id, which is used to associate multiple datasets
derived from a single observation.

My suggestion would be to back up to your previous figure, and replace
ObservationDataset with either "Dataset" (equivalent to what you have
but semantically better defined), or add Dataset below Observation as I
had in my version.  Dataset, or ObservationDataset, should have
attributes such as Type, Subtype, etc.  This would be almost identical
to what I had earlier, except for adding SpectralDM and ObsCoreDM, and
breaking Provenance out as a separate model (this last is arbitrary; it
would work about as well as a submodel like DataID, which is how it is
currently used).

 	- Doug



On Wed, 13 Nov 2013, CresitelloDittmar, Mark wrote:

> All,
>
> Sorry for the frequent image updates.. maybe it would be better to post on
> them on the twiki?
> I modified the connections to improve the class hierarchy.  I think this
> resolves the problem
> I mentioned in the earlier post.  Note. I colored the ObsCore
> generalization blue because it
> is not in the ObsCore document.
>