Observation data model comments

[Pierre Didelon]

Hi Anita and Alberto,
Hi Anita and Alberto,

few comments about history/versionning

I feel that this topic is a crucial one to make selection
inside VO between similar data proposed by diff. providers
(cf prev.mail http://www.ivoa.net/forum/dm/0061.htm).
Data Charaterisation gives you the data state, while history and
versionning will help users to understand how these data
have been obtained. If Processing details are not important
you need only 2 bidirectionnal links (or 4 unidirectionnal links)
between all data for which you want to handle history.
Version and history links in diag.
http://www.ivoa.net/internal/IVOA/IVOADMObservationsWP/root.ps.
Details concerning  history can be added later on, storing
which process (with wich conf.) has produce each data.

Anita Richards wrote:
> On Sat, 8 May 2004, Alberto Micol wrote:
> 
> 

>>---
>>So, the observation is the same, it's the version that changes.
>>(Hence, the requirement is that a VO identifier must be able to handle
>>versioning.)
> 
> I will check if that works in the situations I am thinking of.
> 
I think that aside versioning you need first history to link successive
processing step, then it will be ok!
You have two possibilities  regarding a processing
1) a process give new type/kind of products; it is a 1st version of a prod step,
or 2) a process have the same (or almost) inputs and outputs (only the soft version, or
config param values are diff) then you have a diff. version of an pre-existing data.

nevertheless if this give you a frame where you can store information,
it does not resolve all possible ambiguities. Data producer has to decide inn fine
wether if high spatial-res/low sensitivity and low spatial-res/high sensitivity are
diff. step of analysis (1 :: history branch)
or diff version of of the same production level (2 :: version branch)
I would guess 1!

> 
>>You seem to separate Processing from Provenance. I would have tought that
>>Processing is part of Provenance. Suppose that you want to describe a product
>>which was generated by combining other products coming even from different
>>instruments; in such case I would say that Processing and Provenance are very
>>much intertwined.
>>
> 
> 
> Maybe that is before I put up my latest plot.  I have now put Processing
> back as a part of Provenance but I am still a bit concerned as different
> processing methods will give data with different characterisation e.g.
> different synthesised beam size - for interferometry data you can
> re-weight the visibilities (as many times as you like) to give images with
> lower spatial resolution but greater sensitivity to extended flux (greater
> Max spatial scale) and lower noise rms - or v.v., higher spatial
> resolution but also higher noise and you lose extended flux of low surface
> brightness.  So I am still a bit concerned whether in practice that can
> all be taken care of with versioning.
> 
> 
>>---

Concerning the schema, I don't understand why you have inheritance
between ObsData and MeasuredQuantities and not an historical (processing) link.

a detail; ObsCatalogue is confusing (me at least) with (source) catalog.
ObservationList or ObservationLog wouldn't be better?

Sincerely yours,
-- 
Pierre 
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