[Observation] relation to Dataset

[Douglas Tody]

On Thu, 14 Nov 2013, Arnold Rots wrote:

>> 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?

Multiple Observations can be and often are combined to produce a new
Dataset, however describing that history would be likely be the
responsibility of the Provenance model.  At the level of Observation it
would probably be a new "Observation" (or at least Dataset).  Depends
upon how strict we are with the concept of Observation.  The
CreationType and calibration level say something about it being a
synthesized/derived data product.

> 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.

In practice that is what we are doing, to keep things simple; DataSource
can be something like "theory".

 	- Doug

> Cheers,
>
>  - Arnold
>
> -------------------------------------------------------------------------------------------------------------
> 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/
> --------------------------------------------------------------------------------------------------------------
>
>
>
> 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
>>
>>
>>
>