Dear All,
I'm trying to catch up with UCDs, sorry to be so late.
Matteo's and Ana's comments, plus my own way of reading the list of
words,
and especially the comments associated with each word, make me think
that
something is not yet properly defined, and that some ambiguity is still
to be removed.
While historically UCDs were assigned to *columns* in the Vizier
collection of tables,
I wonder if this is still true. That is, I cannot find in any document
of the UCD1+
the answer to the question:
What is that a UCD can be assigned to?
I know that it CAN be assigned to a scalar quantity;
I know that it CAN be assigned to a column in a table;
but
CAN it be assigned to an image, to a table, or any other piece of
Astronomical Data?
I cannot find the answer in any recent UCD-related document (correct me
if wrong).
I think we need to fill this gap, and give a clear answer.
The answer can be:
NO
--- If the answer is that a UCD can NOT be assigned to anything else than a scalar quantity or an array of identical quantities (i.e., the column in a table), then I do not see why we should have a UCD like instr.interferometry (Thanks Matteo for the good example) YES --- If, at the contrary, UCDs can be assigned to generic, however complicated, data structures then instr.interferometry becomes a nice UCD (though I would suggest data.interferometry instead). Furthermore, if UCDs can be assigned to complex data structures then suddenly I can make sense of other UCDs (like instr.filter.transm) which are currently defined in an ambiguous way:Received on 2005-07-15Z18:33:22
> instr.filter.transm | Filter transmission
Is it for a typical value of the transmission of my filter (e.g. 0.2)? or Does it refer to the entire array that represents the "transmission curve" ? On the other hand, if the answer is YES, then a table could have its own UCDs, (and in that case the VOTable standard will need a revision to support UCDs at the table level). But I think that the answer is NO, because otherwise the vocabulary would need to explode and include all kind of things. Hence, if the answer is NO, then I would suggest to make the comments a bit more strict to avoid confusion. A couple of examples: Current Description Possibly less ambiguous description ------------------- ----------------------------------------- Filter transmission -> Typical value for the filter transmission Spectral resolution -> Typical value of the spectral resolution Resolution -> Typical value of the angular resolution Spectral line -> Common name of the spectral line Detector -> Name of the detector Photographic Plate -> Type of emulsion etc. etc. Alberto PS: Did I get the right answer? Menace: Many more comments to come (e.g. UCDs for Characterisation DM, etc.), hopefully next week.