Hi folks,
I have only a few comments on v1.9.4 - I think it's a great improvement on the previous version, so Roy and Sebastien are to be congratulated. In particular, Section 3.1 is very clear and lays out the path to UCD3 very well.
My first comment picks up something from the discussion leading up to this draft. It was said that we should emphasise that UCD2s are about discovering relevant data, not using them, as that requires more expressive power. If people still believe that, can a sentence to that effect be added in the introductory stuff?...it's in Section 4.1, of course, but I think that the restriction is important enough that it should come earlier, too.
My next comment is just to check something. It seems that "data" has been dropped from the list of basic elements, and "metadata" has arrived. Am I right to assume that "metadata" is now the branch under which I will find the UCDs for recording provenance information? - e.g. versions of data reduction software used, names of astrometric catalogues, etc. If so, that's fine - it's just that that has to go somewhere.
My final comment is my only real concern about this draft, which is whether the examples of Section 3.4 are too ambitious - especially the ones for the error on a right ascension of a galaxy. That seems to be introducing semantics by stealth, and without enough support - i.e. there seems to me to be too much structure in the relationships between those three quantities for UCD2. Maybe I missed it, but is there any semantic distinction to be made between the second and third terms in
stat.error, pos.eq.ra, src.galaxy ?
The third term relates to the second which relates to the third, so if I swap the order of the second and third the meaning is lost.
On the other hand, I'm not sure that the example for photometric colour is good enough, since I don't see how to specify a generic flux ratio between two random passbands - I don't think it's good enough to enumerate the standard optical colours, since, when we federate multiwavelength datasets, I may well be interested in the ratio of a hard X-ray band flux and a K band magnitude, say.
cheers
Bob Received on 2003-10-09Z08:56:23