Late comments (mainly) on the UCD word list

Dear Andrea et al.,

you will find below some comments, mainly on the current UCD list, prepared by Ana and myself. If I interpret correctly your last message to the UCD SciBoard, we have passed the deadline, when the contributions from the UCD SciBoard were expected to come. If so, we have obviously missed some important information about the time-line. We apologize for that. Should our comment be arrived beyond the time horizon, feel free to ignore them for the time being, and to postpone them for the next round of comments, if anyhow interesting:

1. we propose to remove all the words containing an explicit specification of the wavelength or frequency range. They should be replaced by words of the type: "em.wl.start; em.wl.end" (these words do not exist, and should be added). Rationale: the current method lacks flexibility, and is very likely not to cover all the interesting wavelengths ranges in existing catalogues, where "standard" wavelength ranges do not exist (e.g., high-energy)
2. we propose to substitute "instr.${band}" for all words of the type
   "em.${band}". Rationale: the sensitive bandpass is a property of the
   detector
3. we propose to add the words "em.wl.start" and "em.wl.stop". Rationale: they may be useful and flexible characterizations of the bandpass
4. we propose to move "instr.obsty.site.seeing" to "obs.seeing". Rationale: this is a property of an observation rather than of an instrument
5. we propose to unify "instr.beam" and "instr.det.psf" into
   "instr.psf". Rationale: in most cases, users are interested in the
   overall PSF (optics+detector). "Beam" is the radio jargon for PSF. Should the detector PSF be necessary, one could use: "instr.psf; instr.det"
6. we propose to remove "instr.precision". Rationale: too generic, probably useless
7. we propose to add the following radio-related words:
   "instr.interferometry", and "instr.resolution". Rationale: the former is
   self-explaining; the latter indicates the spatial resolution
8. we propose to change the word code of "instr.filter.transm" and
   "instr.spect.resolution" to "V". Rationale: the filter transmission is
   an intrinsically vectorial quantity; the spectral resolution as well (dependence on energy and/or order)
9. we propose to add a further atom to the "Multiplicity of binarity flag": "meta.code.multip.star", "meta.code.multip.planet". Rationale: self-explaining
10. we propose to add a further "meta" atom: "meta.subexp". Rationale: this will allow to characterize the rank of sub-exposures in a multi-exposure observations, whenever useful for, e.g., variability studies
11. we propose to add a further "meta" atom: "meta.rank". Rationale: useful to indicate an element in an intrinsically vectorial quantity
12. we propose to move "meta.id" and "meta.id.assoc" to "src.id" and
    "src.id.assoc". Rationale: they belong to "sources" rather then to
    "metadata"
    
13. we believe that the following "phys" word should be moved to "src":
    "phys.angArea", "phys.AngSize" (and associated words), "phys.area",
    "phys.size" (and associated words). Rationale: the same as #12 above
    
14. we believe that words belonging to the following categories: "phot",
    "pos", "spec", should be placed under the category "src" (e.g.:
    "phot.antennaTemp" -> "src.phot.antennaTemp", "pos.angDistance" ->
    "src.pos.angDistance"; "spect.Doppler" -> "src.spect.Doppler".
    Rationale: all these words ultimately describe source properties
15. the words for coupling of quantum numbers do not cover all the possible coupling cases. A more general method is needed, and the Data Line Model sub-group is indeed working on this. We propose to wait for the conclusion of their work, before this issue is ultimately addressed
16. a new word "pos.offaxis" should be added. Rationale: the off-axis angle may be a useful quantity is some catalogs
17. "pos.earth", "pos.earth.lat", "pos.earth.lon" should be placed under the "obs" category. Rationale: these quantity belongs logically to an observation, not to (the position of) a source
18. "pos.earth.nutation" should be removed. Rationale: it is no longer consistent with the IAU specification
19. a new word "src.ephem" should be added. Rationale: it is necessary to separate "observatory" from "source" ephemeris
20. "spect.veloc" should be replaced by "src.radial.vel". Rationale: it is a property of the source, rather than of a spectrum
21. we propose to add "src.stellarityIndex". Rationale: it may be useful to easily discriminate point-like from extended sources
22. we propose to add the following words in the "stat" category:
    "stat.distribution", "stat.fit.model". Rationale: without them, the
    information on the statistical quantities and/or the fit are incomplete
23. we propose to replace "stat.moment" (as a vectorial quantity) for
    "stat.mean" and "stat.stdev". Any of the statistical moments could be
    therefore indicated by the UCD: "stat.moment; meta.rank". Rationale: the proposed method is more flexible, and could avoid the proliferation of new words to indicate skewness, kurtosis ...
24. the following words should be moved from the category "time" to
    "src": "time.age", "time.crossing", "time.period", "time.phase",
    "time.relax". E.g.: "time.age" -> "src.time.age". Rationale: they
    logically belong to a source rather them to the 4th dimension
25. we propose to add the following word: "time.deadtime". Rationale: useful for photon-counting devices based catalogues

An additional point that we have discussed concerns the units in which interferometric data shall be provided. Is it accepted that data providers have to convert them in physical units at the server level? If not, we need probably to include specific UCD words to deal with
"images" in the Fourier space.

I again apologize for the long and late message. Thanks for your attention.

Regards, Matteo & Ana

-- 
Matteo Guainazzi
XMM-Newton SOC				Matteo.Guainazzi-at-sciops.esa.int
European Space Astronomy Center	of ESA	Phone:     +34 91 8131 176
VILSPA, Apartado 50727, E-28080 Madrid 	Fax:       +34 91 8131 172