CreationType

[Doug Tody]

On Mon, 18 Dec 2006, Alberto Micol wrote:

> Hence, the CreationType actually tells what the data are, not
> what the VO service does on them.

No, DataSource, Collection, etc., (most of the stuff in DataID) tells
what the data are; CreationType refers to the data product returned by
the service and tells what the VO service does to the data source.

> Actually I would prefer a clearer:
>
> vo service input creation type   = spectral extraction
> vo service output creation type  = identity
>
> where 'identity' is meant to say that nothing happened at the service level.

What you call 'identity' is exactly what 'archival' is defined to be:
the same *content* as stored in the archive, without any subsetting,
although the format or serialization may be different ('native' format
is like archival but means the actual data product from the archive).

If the input data is an extracted spectrum, what that mainly means is
that we are accessing a spectrum data collection - many spectral data
collections are composed of extracted spectra, unless the instrument
can directly produce a 1D spectrum.  Even with MOS data the spectra
are often extracted from a 2D detector.  Since there are so many ways
that spectra can be produced before we see them in VO, I think at
the level of SSA should just deal with this with Collection metadata
for now.  That is, you need to go look at the information about the
data collection for details of what it is and how it was generated.
Currently we don't include Collection metdata directly in SSA, rather
one is supposed to use DataID.Collection as a key to go look this
information up in the registry.

If we have an actual spectral extraction SSA service, that is, an SSA
service for which CreationType is 'spectral extraction' that implies
certain things about the service, e.g., the APERTURE parameter can
be used to define the extraction aperture, and the aperture can be
positioned arbitrarily within the DataSource.

 	- Doug