Standards IVOA: UCDs

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Standards IVOA UCDs

• Andrea Preite Martinez
• chairman IVOA WG Semantics

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UCDs IVOA documents (http//ivoa.net/Documents/
)

• An IVOA Standard for Unified Content Descriptors
• v 1.10 - IVOA Recommendation 19Aug2005
• The UCD1 controlled vocabulary
• v 1.11 - IVOA Recommendation 31Dec2005
• v 1.21 - IVOA Proposed Recommendation 7Nov2006
• Maintenance of the list of UCD words
• v 1.20 - IVOA Recommendation 28May2006

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Unified Content Descriptors

• IVOA controlled vocabulary for describing
  astronomical data quantities
• ensure interoperability between heterogeneous
  datasets
• what sort of quantity is this?
• intended to be understandable to both humans and
  computers

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Unified Content Descriptors

• A UCD is a string that contains textual tokens
  that we shall call words, which are separated by
  semicolons (). A word may be composed of several
  atoms, which are separated by period (.)
• UCD wordwordword...
• UCD-word atom.atom.atom...
• The building blocks for UCDs are the words (eg.
  phys.temperature), not the atoms (eg.
  temperature).

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The UCD1 tree

• arith 7 arithmetics
• em 66 electromagnetic spectrum
• instr 31 instrument
• meta 45 metadata
• obs 15 observation
• phot 20 photometry
• phys 120 physics
• pos 69 positional data
• spect 19 spectral data
• src 33 source
• stat 28 statistics
• time 19 time

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• arith
• concepts involving or indicating some math
  operation performed on the primary concept diff,
  ratio, gradient, rate
• em
• description of the e.m. spectrum in bands radio,
  mm, ir, opt, UV, x-ray, gamma
• lines by name (Halpha, Br-alpha,..)
• instr
• quantities related to instumentation detector
  (plate, CCD), spectrograph, telescope, mission

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• meta
• all information not coming directly from a
  measurement (bib, code, id, main, record, ref,
  unit, )
• obs
• quantities describing an observation observer,
  observing conditions, ..
• phot
• photometric measurements flux density, flux,
  magnitude, color(mag diff, or flux ratio)

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• phys
• at mol data
• basic phys. quantities (mass, temperature,
  dimension, luminosity, ..)
• pos
• quantities related to the position of an object
  (coordinates, proper motion, precession,
  parallaxes)
• spect
• spectrophotometric data (kept for historical
  reasons)

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• src
• source classification, variability and orbital
  data
• stat
• statistical information on measurement (error,
  stdev, snr, mean, max, min,..), data fitting, ..
  
• time
• time, date, age

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syntax

• UCD one or more UCD-words
• first word is carrying the basic meaning
• syntax flag
• P words (always primary)
• S words (always secondary) em_bands
• Q/E/C/V words quantities
• phot.flux.densityem.radio.750-1500MHz (ESS)
• stat.errorphot.magem.opt.Bem.opt.V (PCSS)
• phys.velocpos.cartesian.z (VQ)

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Tools... (http//vizier.u-strasbg.fr/UCD/)

• assign (from description in normal language)
• validate (spelling, syntax)
• explain (description)
• upgrade (for deprecated words)
• translate (ucd1 gt ucd1)
• web services

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tools... (http//vizier.u-strasbg.fr/UCD/cgi-bin
/descr2ucd)
P_words Q/E/C/V_words S_words
syntax
semantic rules
description
find_word
build_ucd
P stat.error Q pos.pm.dec
standard error of proper motion in declination
stat.errorpos.pm.dec
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batch assignator

• assign1p exploits the information in
• Description
• Units (not fully implemented!)
• Column name
• Notes
• to generate a working description to which
  semantic rules (gt300) are applied
• finds ucd-words best matching the std list
• builds ucd (100 syntactic rules)

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batch assignator

• plus
• speed all vizier in lt 8 (173,000 assignations)
• efficiency assigns in 99,3 of cases
• magics
• Count rate in the hard ROSAT window 0.1-2.4keV
• arith.ratephot.countem.X-ray.soft
• uncertainty flag Y-Z
• meta.code.errorphot.colorem.opt.Bem.opt.V

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batch assignator

• minus
• speed all vizier in lt 8 (but weeks to check!!)
• efficiency real rate lt80
• magics (?)
• RVel ? spect.dopplerVeloc
• RV ? ??
• code written by amateur
• incomplete set of rules
• units not fully exploited
• dimensions not yet used