ImageDM/ObsCore - Dataset

[CresitelloDittmar, Mark]

All,

I thought that I would elaborate on a point in the diagram I sent out
the other day:

ImageDM - ObsCore Convergence thread.
  http://www.ivoa.net/pipermail/dm/2013-October/004778.html

In that diagram, Observation contains 'dataset specific' metadata such as
dataProductType and calibLevel.  In the extension, those items move into a
'Dataset' object.

I did this to resolve, what seems to be a disconnect between the model
description (text), and mapping (utypes).

>From the description, it seems clear that the intent is that an Image or
Spectrum *is* a Dataset.. with particular characteristics (dataProductType,
dataProductSubType, Length).

In Observation, those items are attributes of the top level object
"Observation"
  - but the utypes contain a "Obs" node

The Observation object also *has* a Curation, DataID, Target.
  - none of those have a 'Obs' node in their utypes.

In the old "Spectrum" model, some of these were at the top level too
"Spectrum.Length".   When we removed 'Spectrum' node, these went to a
Dataset object to avoid "Length" for a utype.

So to keep the mapping and model consistent, it seems necessary to have the
top
level object be a container of objects at the same level covering the
different topics.  And so, we have a Dataset object containing dataset
specific metadata.

Mark
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