UCDs at the HEASARC - IVOA

							INTERNATIONAL VIRTUAL OBSERVATORY ALLIANCE




     HEASARC Experiences with UCDs
       Tom McGlynn and Michael Preciado, NASA/GSFC




                    Tom McGlynn NASA/HEASARC   5/18/2006   1
What do we see as the purpose of
UCDs?

  • Discovery: Need to find tables that address a
    particular question.
  • Analysis: How do I understand a table that I have
    retrieved.
  • Identification: Mark specific columns in a table
    (SIA, Cone search)
     – To be superseded by UTYPE?


  Concentrate efforts on columns of a table that will
    be of interest generally.



                     Tom McGlynn NASA/HEASARC   5/18/2006   2
Minor issues.

  • Non-specific UCDs
    – Meta.number, meta.note, meta.code
      • Does this convey more information than just a
        blank UCD?
  • Ambiguities
  • When do we settle for an OK UCD, when
    do we need to get a better one?




                    Tom McGlynn NASA/HEASARC   5/18/2006   3
The Observing Process

 •   UCDs defined for ‘object’ tables not for ‘observation’ tables.
 •   Current UCDs handle the details of the actual observation but not of the
     entire observing process.
      –   Proposed, scheduled, actual, ...
            • Add adjectives like: obs.proposed, obs.scheduled (e.g., time.expo;obs.proposed) with
              implicit default of obs.actual or some such)
      –   Times: Readout time, download time, release date,...
            • Probably requires new nouns
      –   Processing status, software configuration used, calibration status, revision, ...
            • Does this belong in obs or perhaps a new processing tree.
                  –   Obs.calib is already there but not clear how to use it in this context)
                  –   Proposal cycles
      –   Information that links to archive
            • Part of obs tree?
            • Obs.data.filename (and maybe obs.data.filename;obs.calib for calibration data?)
      –   Datatypes, data sizes
            • Maybe a generic concept here, modified by the appropriate context
            • File.size;obs.data.filename [maybe comp.file.size;obs.data]
 •   These are concepts that users are very much interested in...




                                        Tom McGlynn NASA/HEASARC                                5/18/2006   4
Miscellaneous concerns

 • Can we build new UCDs from existing words?
 • Have UCDs for semimajor and minor axes. Do we need to
   use different UCDs for major and minor axes [versus
   semi...]?
 • Bands in X-ray and gamma-ray regimes. The distinction
   between hard and soft gamm-rays does not accord well
   with current usage. E.g., for EGRET and GLAST, hard
   implies > ~50 MeV not 500 keV.
 • How do we do upper limits? How do we distinguish upper
   limits from upper bounds? Stat.max for both?
 • Meta.id versus meta.id.cross versus meta.id.assoc – how
   systematic before we use the second, how distinct before
   we use the third?
 • Phys.absorption versus phot.color.excess




                     Tom McGlynn NASA/HEASARC   5/18/2006     5
Misc. cont’d.

  • Meta.bib versus meta.ref
  • Why spect.dopplerVeloc.opt rather than
    spect.dopplerVeloc;em.opt?
  • Counts/densities of nearby sources
  • V/Vmax (some kind of stat but I don’t know
    what).
  • Opacity of source
  • Instrumental characteristics versus instrument
    settings
  • Can any numeric quantity actually be just
    primary?
     – (Given X can’t I always have: stat.err;X)



                       Tom McGlynn NASA/HEASARC    5/18/2006   6
Summary

 • Most columns we can find UCDs for.
 • There are major holes in the handling of
   observation tables
 • Hard to understand the real boundaries
   between UCDs.




                Tom McGlynn NASA/HEASARC   5/18/2006   7
Concern

 • How do I search for UCD matches.
 • Can I do this mechanically?
   – Does a.b match a.b;c.d
   – Does a;c.d match a.b;c.d
 • Does making UCDs more specific make it
   harder to get matches?




                 Tom McGlynn NASA/HEASARC   5/18/2006   8