While characterization model is in the last steps of the recommendation process
why don't we take a break?
While building characterization version 1, we faced a lot of times use cases
including descriptions of observations which were falling outside the scope of
our original limited goals in this model.
If IVOA standards are to be usefull we have now to rapidly take into account
these use cases, prioritarize them and start to adress them. Some still belong
to the characterization effort at detailed levels . Some others will address
only the Provenance description of observations.
1 Spectroscopic and Photometric data for SED building and cross calibration need :
Apertures, Beam (or PSF) are needed for comparison.
as well as Photometric calibration in the form of transmission curve of the
filters and zero points
2 Transmission curves in general will be also very usefull for characterizing spectral and flux axes of 2D images, or catalogs seen as "datasets" either to get good photometry of extracted sources or surface photometry.
3 Many datasets can be seen as compositions of simple observations ( multi CCD cameras, IFU) But both the characterization of the whole and of the component may be necessary. Resolution may change from one block to the other one.
An IFU may have varying spectral range and resolution on the field, we may need
to characterize that, as well as keeping the spatial and temporal characterization of
the whole IFU in common
4 the Dataset we consider is generally a moment in a process of transformation from
very raw data to high level extracted information or visualisation.
For quality assesment it could be usefull to get raw data and calibartion data linked to the reduced dataset in order to make some comparisons or do some kind of reprocessing. Description of the programs is also part of this
4 bis A similar case is the stacking of reduced data in one "association" to improve the SNR or remove artifacts. links between the stack, the members and a description of the stacking algorithm is usefull.
4 ter Dataset transformation may also be needed to provide convenient visualizations
usefull for data discovery or analysis
Again these visualizations have to be linked to the transformation description as well
as to the progenitor dataset.
WCS information is generally conveyed with the data using Pre-VO technology such as FITS keywords. It is probably usefull to be able to describe this kind of mapping observation within the frame of a general Observation datamodel.
Use case 1,2 3 belong to what would be called in IVOA vocabulary enhacement of charcaterisation model by better specifiaction of level 4 or characterisation of complex data. Use case 4 and 6 and maybe 5 belongs more to what is called by many people "Provenance". of course this is not and cannot be exhaustive.
We have to start reviewing exsiting modelling of such aspects: (original IVOA observation data models, the small Acces and Views datamodel, Pat Dowler and G Lemson domain model, the new CADC Observation model, plus more specific models such as Radio data models, etc.) and decide a strategy of reuse and development to perform this next step of our modelling effort
Many of these use cases will also have consequeneces ifor the definition of new generation DAL protocols such as SIA2, TAP and Complex data Access.
François Bonnarel
Francois Bonnarel Observatoire Astronomique de Strasbourg CDS (Centre de donnees 11, rue de l'Universiteastronomiques de Strasbourg) F--67000 Strasbourg (France)
Tel: +33-(0)3 90 24 24 11 WWW: http://cdsweb.u-strasbg.fr/people/fb.html Fax: +33-(0)3 90 24 24 25 E-mail: bonnarel-at-astro.u-strasbg.fr ---------------------------------------------------------------------Received on 2007-09-26Z17:17:16