Observation data model comments

Sat May 15 15:15:17 PDT 2004

Salut Pierre, Hello Anita, Hi there,
    It seems that it was one thousand years ago.
    Hey, no, May 10th 2004 not 1004, that's only 6 days!
    But so much emails in the mean time!

<From owner-dm at eso.org  Mon May 10 17:37:39 2004
<X-Authentication-Warning: mercury.hq.eso.org: majordomo set sender to owner-dm at eso.org using -f
<Date: Mon, 10 May 2004 16:41:00 +0100 (BST)
<From: Anita Richards <amsr at jb.man.ac.uk>
<X-X-Sender: amsr at megahard
<To: Pierre Didelon <pdidelon at cea.fr>
<cc: dm at ivoa.net, radiovo at ivoa.net
<Subject: Re: Observation data model comments
<
<I think Francois will reply more, just a somment:
<
<> I am not sure to catch your point.
<> For me each data (ObsData, ProcessData...) has it's own Characterisation.
<>  From your comment it seems that you suppose that Characterisation is linked
<> to only ObsData (raw data or data sufficently related to it, to have
<> the same Characterisation). But then how do you handle Characterisation
<> for data processing which changes this considerably, like in your example
<> with high/low  spatial-res/sensitivity  outputs.
<> Or do I missed something?
<
<No, that is exactly my problem, which I thought that Versioning was
<suggested to overcome.  At the moment VOs are probably only usefully able
<to handle a few sorts of data from any one provider, and that should not
<be too raw - I think that ObsData can be _anything_ but in general if it
<is of any use to the VO it will be data ready for analysis, e.g. source
<extraction.  That is, it is data which has had the instrumental
<characteristics taken out of it and can be analysed using generic tools.
<(Of course we make all sorts of exceptions like keeping zero-points for
<HST wavebands...)
<

-----> I think ObsData is there for "Data belonging to this Observation"
and can be attached to any kind of Observation described in the introduction
of the Draft. (including raw and processed observation".) 
     This OBsData is a specialisation    of "Quantity".
    Actually anything in the Observation components is static and associated
to the Observation at this very time. Everything except the Processing which 
is in Provenance and which has to be historical. The processing is probably
the class where the link to other observations giving birth to the one
we are looking 	at, has to be made. It is through Processing that the
 recursivity of the Observation class is travelling !
Anita , you illustrated that via  your VLA + MERLIN composition example.
Hence the "two Observation box" you are surprised by, Pierre.
>From Observation to Processing (or composition = specialisation) it should
be an association I guess.   While Processing is agregated in Provenance
In my mind.

Another thousand years and we will all meet in Boston.

Cheers/Amitiés
François

<>
<> I didn't understand either the two Observation box, and the link between
<> them? ?association between Observation and Provenance => simple line
<> (change needed?) ?agregation/composition between Provenance and
<> Processing => diamond+line (ok) ?inheritance/specialisation between
<> Processing and Composition => triangle+line (change?) ?agregation or
<> association between Composition and Observation => change or not?
<
<Maybe I should have just left everything with plain lines, if my arrows
<don;t make sense just ignor them as they are probably wrong.
<
<> But perhaps a clear gap has to be made between data directly obtained from
<> observation (related to only ONE observation, a set of data which shares prov.)
<> from the ones deduced from confrontation/agregation of several observation.
<> However it seems to me that such a separation is artificial, and sometimes
<> not realistice. For example calibration of bservational data uses elaborated
<> data deduced from previous experiment and so on.
<
<Absolutely, there is no clear indivisible unit, it has to be flexible as
<you say.
<
<>
<> PS : As pure intelectual curiosity what are the units of the 7D of
<> visibility data? Did yu have any ref. or doc available and usable for a
<> beginner in radio data like me?
<
<example
<
<AIPS 1: COMPLEX      3   0.0000000E+00       1.00  1.0000000E+00    0.00
<AIPS 1: STOKES       2  -1.0000000E+00       1.00 -1.0000000E+00    0.00
<AIPS 1: FREQ       255   2.2235079E+10     128.00  7.8125000E+03    0.00
<AIPS 1: IF           1   1.0000000E+00       1.00  1.0000000E+00    0.00
<AIPS 1: RA           1    00 00 00.000       1.00       3600.000    0.00
<AIPS 1: DEC          1    00 00 00.000       1.00       3600.000    0.00
<
<
<Complex covers the visibility plane, Stokes is polarization (usually
<either LL and RR or just one, or LR and RL, or IQUV), FREQ is frequency
<channels IF is when you have a number of frequency bands (each with e.g.
<255 channels)
<
<In addition in the visibility plane you have
<UU-L  VV-L  WW-L
<which are derived from
<BASELINE  TIME1
<and FREQ
<and
<SOURCE
<
<COnfused? So am I...
<
<Most of the guides to interferometry start with an idealised
<interferometer not with the data representation. Paddy Leahy's chapter in
<the MERLIN User Guide is the shortest version of that I ahve seen:
<http://www.merlin.ac.uk/user_guide/OnlineMUG/newch0-node30.html
<
<or for general data representation with radio interferometry examples see
<the (perm any author combination) Greisen Calabretta Valdez WCS papers -
<you probably know far more than me already but if not see
<http://www.aoc.nrao.edu/~egreisen/index.html
<(bottom of page, under all the birds)
<
<all the best
<
<Anita
<

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Francois   Bonnarel               Observatoire Astronomique de Strasbourg
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