[Observation] relation to Dataset

[Arnold Rots]

>From this description I am beginning to suspect that a Dataset can be
derived from
(associated with) no more than one Observation.
That seems utterly wrong; multiple Observations can be combined into a
single Dataset.
Or did I misunderstand?

I think it is OK to require that a Dataset is associated with at least one
Observation,
provided that a model or simulation can be described as an Observation.

Cheers,

  - Arnold

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Arnold H. Rots                                          Chandra X-ray
Science Center
Smithsonian Astrophysical Observatory                   tel:  +1 617 496
7701
60 Garden Street, MS 67                                      fax:  +1 617
495 7356
Cambridge, MA 02138
arots at cfa.harvard.edu
USA
http://hea-www.harvard.edu/~arots/
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On Thu, Nov 14, 2013 at 12:08 PM, CresitelloDittmar, Mark <
mdittmar at cfa.harvard.edu> wrote:

> All,
>   This thread is for discussion on the relation between Observation and
> Dataset.
>
> ref: ObsCoreDM - http://www.ivoa.net/documents/ObsCore/20111028/index.html
> ref: diagram illustrating relation of Image/Spectral Observation to
> ObsCoreDM (draft)
>
> http://www.ivoa.net/pipermail/dm/attachments/20131113/c9ef7581/attachment-0001.png
>
> motivation
>   It is clear that there is a relationship between "Observation" and a
> more generic "Dataset".  This "Dataset" would contain elements such as the
> dataProductType, and dataProductSubtype, presumably others.  This object
> has not been formally defined.
>
>   In ObsCore, there is an implied relationship for Observation as an
> Extension of Dataset in the location of these attributes.  So, I have
> always interpreted that Observation "is" a Dataset.  This is reflected in
> my choice of the name "ObservationDataset" in the left hand package of my
> diagram.  It implies that it is a Dataset extended for Observation purposes.
>
>   Recent discussion brings this relationship into question, with
> assertions that an Observation can be associated with 0 or more Datasets.
>
>   This has real ramifications for the Image and Spectral models..
>
> Seed:
>
> If the relation is Observation "has" 0..* Dataset, then all the diagrams
> to date are wrong.
> It feels like this would be a fundamental change to all these models.
>
>   - there would need to be a bi-directional relation between Observation
> and Dataset
>        (observation has 0..* Dataset; Dataset associated with 1
> Observation)
>     Hmm.. since there can be Datasets not associated with Observations,
> this would
>     need to be a specialization of Dataset.. (ObservationDataset.. but not
> the one in my diag.)
>
>   - the Char associated with Observation would characterize the total
> space of all included Datasets.  (0..1) relation to Observation.  If no
> Datasets, no Char
>
>   - each Dataset would require it's own Characterisation, specific to it's
> space.
>     (so there is another attribute for Dataset).
>
>   - we would need to specify which of the elements are associated to the
> Dataset, and which to the Observation.  e.g. DataModel => Dataset;  Target
> => Observation
>
> Thoughts?
> Mark
>
>
>
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