UCD1+ controlled vocabulary - Updated List of Terms

Official bibliographic entry for published version [UCDlist1.2].

Status:

UCDlist 1.6 EN 2024-12-18

1 Introduction

A UCD is a string which contains textual tokens called ‘words’, separated by semicolons(;). A word is composed of ‘atoms’, separated by periods(.). The hierarchy is as follows:

\[\textrm{atoms} \rightarrow \textrm{words} \rightarrow \textrm{composed words}\]

UCD1+ are either single words, or a composition of several words.

UCDs are “controlled” through a process defined in the IVOA. See Derriere et al. [UCD1.1] and section A.2 Definition of words below. Control is exercised at the level of words (UCD1+) and at the level of the vocabulary (atoms) used to form words. A consistent list of atoms will be maintained, making sure that the same atom always means the same thing, even if used in combination with different other atoms.

2 List of valid words

All words are preceded by a ‘syntax’ code that can help in the process of building composed UCD1+.

  1. “P” means that the word can only be used as “primary” or first word;

  2. “S” stands for only secondary: the word cannot be used as the first word to describe a single quantity;

  3. “Q” means that the word can be used indifferently as first or secondary word;

    The following cases behave as Q prefix and can be combined as primary or secondary. They specialize the combination rules:

    1. “E” means a photometric quantity, and can be followed by a word describing a part of the electromagnetic spectrum;

    2. “C” is a colour index, and can be followed by two successive word describing a part of the electromagnetic spectrum;

    3. “V” stands for vector. Such a word can be followed by another describing the axis or reference frame in which the measurement is done.

For typographic reasons some long UCD atoms are printed on two lines in the following table. In these cases, some.long... ...ucd.x is to be read as some.long.ucd.x.

Appendices

A Definition of atoms and words

A.1 Definition of atoms

Atoms are defined following these guidelines:

  1. Abbreviations are used in contexts where their meaning is unambiguous. (ra, dec are acceptable, but t is ambiguous: time and temperature are used instead.)

  2. Atoms are not hyphenated. The separation is marked by a capital letter to help readability (position angle = posAng) unless the composed word has a well- known acronym (signal to noise ratio = snr) or short form (standard deviation = stdev). There are only two exceptions to this rule: (i) the X-ray band (em.X-ray) and (ii) the frequency / wavelength intervals defining regions of the e.m. spectrum (e.g., em.radio.3-6GHz).

A.2 Definition of words

The list of UCD1+ words is evolving following the requirements of new datasets distributed in the IVOA ecosystem. The last iteration on the list included new terms for planetary data and was published in an IVOA REC specification [UCD1+1.3].

It is maintained following advice from a UCD Scientific Board, and published as an Endorsed Note from version 1.4 onwards following the procedure recommended in [UCDlistMaintenance2.0].

B The structure of the UCD1+ tree

All existing UCD1+ words are grouped into 12 main categories. These categories are expressed by the first atom of the word, whose possible values are:

  1. arith (arithmetics)
    This section includes concepts involving or indicating some mathematical operation performed on the primary ‘concept’ or just the presence of an arithmetic factor or operator.
  2. em (electromagnetic spectrum)
    This section describes the electromagnetic spectrum, either in a monochromatic way or in predefined intervals. The complete list of proposed bands (in seven classical regions of the electromagnetic spectrum: radio, millimetre, infrared, optical, ultraviolet, x-ray and gamma- ray), can be found in the document https://wiki.ivoa.net/internal/IVOA/IvoaUCD/NoteEMSpectrum-20040520.html
  3. instr (instrument)
    This section includes all quantities related to astronomical instrumentation, e.g. detectors (plates, CCDs, etc.), spectrographs, and telescopes (including observatories or missions), etc.
  4. meta (metadata)
    This section includes all the information that is not coming directly from a measurement, and information that could not be included in other sections.
  5. obs (observation)
    In principle under this section should go all words describing an observation (the name of the observer or PI, the observing conditions, the name of the field). In practice, this section helps to identify concepts related to an observation process.
  6. phot (photometry)
    All the words describing photometric measures are included in this section. The definitions distinguish between a flux density (flux per unit frequency interval), a flux density integrated over a given electromagnetic spectrum interval (flux if expressed linearly, mag if expressed by a log), or a flux expressed in counts/s (if the setup of the detector is photon counting observing mode). ‘Colors’, which are differences of magnitudes (i.e. ratios of fluxes) measured in different bandpasses, are also included.
  7. phys (physics)
    This section includes atomic and molecular data (mainly used for spectroscopy) and basic physical quantities (temperature, mass, gravity, luminosity, etc.)
  8. pos (positional data)
    This section describes all quantities related to the position of an object on the sky, or on a celestial body:

    • Angular coordinates, and projections from spherical to rectangular systems.

    • Angular measurements in general (the angular size of an object is in this section, its linear size is in the phys section).

    • The World Coordinate System FITS keywords.

  9. spect (spectral data)
    For historical reasons, photometric data taken in narrow spectral bands with instruments called spectrographs are classified as spectroscopic data (spect). These definitions should not be confused with those in the em category: em represents the independent variable, or dispersion axis; whereas phot and spect describe dependent variables, like a flux density under the phot branch, or a spectral line intensity in the spect branch.
  10. src (source)
    This is a rather generic section, mainly devoted to source classifications. Variability, orbital, and velocity data are also included in this section.
  11. stat (statistics)
    This section includes statistical information on measurements.
  12. time (time)
    Quantities related to time (age, date, period, etc.) are described in this section.

C Combining UCD words

C.1 Goal

Since their definition UCDs have been used in major catalogue archives, in the definition of various VO protocols (SSA, SIAv2, SLAP, TAP ObsTAP, EPN-TAP, etc.) and used with success to provide semantic annotation for a huge collection of table columns distributed in the astronomical community.

The list of terms has increased and the usage of UCD combination has become very common. This leads to a richer set of rules in the assigning and checking tools developed at CDS with VO partners.

In order to keep the consistency in the UCD thesaurus, each rule is adjusted and weighted considering the physical usage of the quantities represented in table columns, so the pertinence increases with the context. Initially used for source catalogues (Vizier, Heasarc archives, etc.) in the first place, they are now also used in VOTable documents for planetary data [EPNTAP2.0] and all sorts of metadata.

C.2 Remarks on combination rules

The combination rules have been defined in the first IVOA documents defining UCD concept [UCD1.1] and refined in the last UCD1+ standard recommendation [UCD1+1.3]. They are exposed with a syntax code given as a property of each UCD word and included in the list of UCD words. See Section 2 List of valid words with the codes definitions on top.

They correspond to real usage of the terms in science publications and are assigned to catalogue columns by experienced data scientists. UCD combination also reflects the catalogues build-up strategy. Errors and statistics, for instance, are provided with measurement values; measures and model comparison are evaluated with error fits, precision, etc. All the scientific knowledge helps to define appropriate UCD words combination.

The assigning tool proposed at http://cds.u-strasbg.fr/UCD/cgi-bin/descr2ucd is based on the pragmatic encoding of physical quantities found in science papers and data attached to publications.

D Current questions about combinations of UCDs

D.1 How do UCDs differ from structured descriptions?

UCDs do not provide a structured representation of table content but the meaning or relative class concept known at the time for the astronomical speciality. Therefore, the structure of words and their rules for combination do not follow any object oriented paradigm, in contradiction to any reference to a data model item (Utype, VO-DML type /role definition), which are dependent of a defined and endorsed IVOA data model specification.

D.2 P or S syntax code: Which is the most pertinent position for a UCD word?

P, S and Q are the labels expressing in which position of a UCD expression a term can be used, P in first place, S as suffix, and Q in both allowed position: head and tail. The UCD list defines the recommended position for each word with some flexibility.

P is always what matters the most to describe a quantity, i.e., the kind of property that should be searched for in primary order, and the most relevant UCD words to represent a quantity.

S is the code for the qualifying part of the UCD, the secondary information appended to specify the first UCD term.

Examples:

  • Give me all columns / all catalogues with a column having a magnitude in R: magnitude is the primary concept and band R is the secondary concept, so the ucd to search for is phot.mag;em.opt.R.

  • Give me all columns with an error on magnitude B: here we shall use a query with ucd equals to stat.error;phot.mag;em.opt.B. Here the main concept attached to the column value is error, qualified by phot.mag, itself qualified by em.opt.B.

Concatenation can apply more than one time, depending on ordering rules. See Derriere et al. [UCD1.1], section 3.3, for other details.

E Associated Files

This document comes with two plain text files: ucd-list.txt [1] and ucd-list-deprecated.txt [2]. Their content is described below.

To simplify the distribution of these files with common software products, they are distributed under the Creative Commons CC0 public domain dedication. [3]

E.1 UCD List file

The ucd-list.txt file is a plain text formatted table with three columns. It is the source file of Table UCDlist:table:ucd-list. It contains all UCD terms validated for this version of this IVOA Note.

The columns are separated by | (pipe) characters. From left to right, the columns contain, respectively, the positional syntax code, the UCD word, and its standard definition.

E.2 Deprecated UCD List file

The ucd-list-deprecated.txt file is a plain text formatted table with two columns separated by a whitespace character. The first column contains the deprecated UCD words, while the second contains the UCD term that should be used instead.

E.3 Comments in file

Comment lines are starting with a # (hash) character.

E.4 Version tags in companion lists of terms: ucd-list.txt and ucd-list-deprecated.txt

The first line of each of these files is a comment line containing the UCDList version tag following the pattern #$DOCTYPE-$DOCNAME-v$DOCVERSION-$DOCDATE, where the variable names are taken from the Makefile defined by ivoatex []. For a pre-release list, such a first line might look like #PEN-UCDlist-v1.5-20220706.

Solely the lists with version starting by EN-UCDList are valid reference for UCD terms or deprecated terms. They correspond to the Endorsed Note at the final step of the update cycle. Others are only work-in-progress and are only intended for review. They should, in particular, not be distributed with external software products.

F Changes from previous versions

F.1 Changes from UCDList EN v1.5 following RFM

F.1.1 Additions

  • meta.coverage

  • time.period.pulsation

  • stat.confidenceLevel

  • stat.falseNegative

  • stat.falsePositive

  • phys.inspiralSpin

  • phys.voltage

Atmospheric measures at the telescope site :

  • obs.atmos.humidity

  • obs.atmos.rain

  • obs.atmos.turbulence

  • obs.atmos.turbulence.isoplanatic

  • obs.atmos.water

  • obs.atmos.wind

  • phys.temperature.dew

F.1.2 Amendment

  • Change positional syntax code of stat.stdev to Q in order to combine it to stat.confidenceLevel, for instance

  • Change positional syntax code of from E to Q.

F.1.3 Deletion

Deprecate term pos.lambert (appearing in one table only) and propose pos.projection instead. In the future setting up a VO vocabulary to record projection names and identifiers together with the associated parameters if needed, as defined in the Calabreta and Greisen FITS Paper [] on table 13.

F.2 Changes from UCDList EN v1.4 following RFM

F.2.1 Additions

, ,:raw-latex:ucd{stat.mad}
, , ,

F.2.2 Amendment

  • Amending changed to Q to allow combination as secondary term. The former usage for the id or name of a curator is discouraged. is recommended instead.

  • Amending description with “related to” to make it work better as an S atom.

F.2.3 Associated lists

Added version tags in associated list files: ucd-list.txt and ucd-list-deprecated.txt.

F.3 Changes from REC v1.3 following RFM

The document title has been updated and the document sections have been reorganised to focus on the list of terms, moving UCD1+ standard reminders to Appendix sections.

The modifications decided during the UCD1+ list v1.3 RFM [4] process are presented below.

F.3.1 Additions

F.3.2 Clarification

Clarified position rules for syntax code E, C, V in Section 2 List of valid words.

F.4 Changes from PR v1.3-2018 following TCG comments

F.4.1 Update of definitions

F.4.2 Changes of position indicator

Was

Changed to S to conform to the “Related to” definition and the usage of this UCD, mostly appearing as suffix.

F.5 Changes from WD v1.3-20160719

Added section 3 Remarks on combination rules for UCD words.

F.5.1 New terms

F.6 Changes from WD v1.23-20160719

F.6.1 Additions

F.6.2 Amendments/clarifications

Definition for

  • phys.area Area (in surface, not angular units)

  • stat.stdev Standard deviation as the square root of the variance

F.7 Changes from WD v1.23-20150608

Text of Abstract, last two lines. Added reference to .

Section 1.1 Definition: “Abbreviations are used in contexts where their meaning is unambiguous” instead of “kept to a minimum…”

F.7.1 Amendments/clarifications

F.7.2 Additions

F.7.3 Deletions/replacements

  • deleted: em.UV.FUV

  • deleted: phys.mol.qn; replaced by: phys.atmol.qn

  • deleted: pos.bodyrc.long; replaced by: pos.bodyrc.lon

  • deleted: pos.eop.nutation; replaced by: pos.nutation

F.7.4 Deprecated

  • meta.ref.ivorn: The term IVORN should not be used any more for IVOA Identifiers (IVOIDs). In UCDs, meta.ref.ivoid should be used instead.

F.8 Changes from PR v1.22

Text of pararagraph 1.1 (2), last three lines;

List of em bands reordered according to wavelength/frequencies.

F.8.1 Amendments/clarifications

Description changed in words: phys.atmol.qn

F.8.2 Additions

em.line.Hdelta, em.line.Lyalpha, em.line.CO.

F.8.3 Deletions/replacements

  • deleted: phys.mol.qn; replaced by: phys.atmol.qn

F.9 Changes from PR v1.21

F.9.1 Amendments/clarifications

  • Syntax code changed in words: phys.polarization

F.10 Changes from PR v1.2

F.10.1 Additions

  • spect.continuum

F.11 Changes from REC v1.11 (Rec20051231)

F.11.1 Amendments/clarifications

  • Spelling: phys.atmol.sWeight

  • Syntax code changed in words: phys.atmol, spect.line

F.11.2 Additions

F.11.3 Deletions/replacements

  • deleted: phys.atmol.damping; replaced by: phys.damping with description: Atomic damping quantities (van der Waals)

  • deleted: phys.atmol.qn.I; replaced by: phys.atmol.qn with description: Nuclear spin quantum number

  • deleted: time.event; replaced by: time.duration with description: Duration of an event or phenomenon

  • deleted: time.event.end; replaced by: time.end with description: End time of event or phenomenon

  • deleted: time.event.start; replaced by: time.start with description: Start time of event or phenomenon

  • deleted: time.expo; replaced by: time.duration;obs.exposure with description: Exposure on-time, duration

  • deleted: time.expo.end; replaced by: time.end;obs.exposure with description: End time of exposure

  • deleted: time.expo.start; replaced by: time.start;obs.exposure with description: Start time of exposure

  • deleted: time.obs; replaced by: time.duration;obs with description: Observation on-time, duration

  • deleted: time.obs.end; replaced by: time.end;obs with description: End time of observation

  • deleted: time.obs.start; replaced by: time.start;obs with description: Start time of observation

F.12 Changes from v1.10

  1. A few minor changes to the text have been done

  2. All UCD words are now compliant with the UCD recommendation. The corresponding changes are described below

  3. The following words have been deprecated:

    New corresponding UCD

    sptablerule

    Deprecated UCD

    phot.flux.density

    sptablerule

    phot.fluxDens

    phot.fluxDens.sb

    phot.flux.density.sb

    phys.at*

    phys.atmol*

    phys.atmol.coll

    phys.atmol.collisional

    phys.atmol.ion

    phys.atmol.ionStage

    phys.atmol.trans

    phys.atmol.transition

    phys.energyDensity

    phys.energy.density

    phys.massToLight

    phys.composition.massLightRatio

    phys.massYield

    phys.composition.yield

    spect.doppler

    spect.dopplerParam

    sptablerule

  4. The following word has been created: phys.composition

  5. The section Changes from previous versions has been reformatted

F.13 Changes from v1.0

  1. Descriptions have been changed for the following words: em.line, instr.pixel, phys.gravity, pos.earth.altitude

  2. The syntax codes changed for words: instr.filter, phys.angSize

  3. The following words have been deprecated:

    New corresponding UCD

    sptablerule

    Deprecated UCD

    phys.transm;instr.filter

    sptablerule

    instr.filter.transm

    phys.mass.light

    phys.massToLight

    pos.resolution

    pos.angResolution

    pos.satellite

    pos.bodyrc

    sptablerule

F.14 Changes from v1.01

The following words have been restored to their previous spelling (v1.00):

A note has been added to indicate that these words do not strictly comply with the UCD1+ Rec.

F.15 Changes from v1.00

  2. The following words have been deprecated:

    New corresponding UCD

    sptablerule

    Deprecated UCD

    pos.resolution

    sptablerule

    instr.angRes

    instr.obsty.site

    pos.earth.altitude;instr.obsty

    instr.obsty.site.seeing

    instr.obsty.seeing

    instr.spect

    instr

    instr.spect.dispersion

    instr.dispersion

    instr.spect.order

    instr.order

    instr.spect.resolution

    spect.resolution

    instr.tel.focus

    instr.tel.focalLength

    meta.fits.software

    meta.software

    obs.air

    obs.atmos

    obs.air.extinction

    obs.atmos.extinction

    obs.air.mass

    obs.airMass

    phot.fluxDens

    phot.fluDens

    phot.fluxDens.sb

    phot.fluDens.sb

    phot.sb

    phot.mag.sb

    phys.at.branchingRatio

    phys.atmol.branchingRatio

    phys.at.crossSection

    phys.atmol.crossSection

    phys.at.lineShift

    phys.atmol.lineShift

    phys.at.moment

    phys.at.moment.electric

    phys.at.radiationType

    phys.at.moment.magnetic

    phys.at.radiationType

    phys.at.qn.S

    phys.at.qn

    phys.at.qn.L

    phys.at.qn

    phys.at.qn.J

    phys.at.qn

    phys.at.qn.F

    phys.at.qn

    phys.atmol.state.final

    phys.atmol.final

    phys.atmol.state.initial

    phys.atmol.initial

    phys.massYield

    phys.mYield

    phys.mol.quadrupole.magnetic

    phys.at.radiationType

    phys.refraction

    phys.refractIndex

    pos.az.ha

    pos.eq.ha

    pos.earth.nutation

    pos.eop.nutation

    spect.veloc

    spect.dopplerVeloc

    src.fwhm

    phys.angSize;src

    src.orbital.veloc

    phys.veloc.orbital

    src.veloc

    phys.veloc

    src.veloc.ang

    phys.veloc.ang

    src.veloc.cmb

    phys.veloc;pos.cmb

    src.veloc.dispersion

    phys.veloc.dispersion

    src.veloc.escape

    phys.veloc.escape

    src.veloc.expansion

    phys.veloc.expansion

    src.veloc.lg

    phys.veloc;pos.lg

    src.veloc.lsr

    phys.veloc;pos.lsrv

    src.veloc.microTurb

    phys.veloc.microTurb

    src.veloc.pulsat

    phys.veloc.pulsat

    src.veloc.rotat

    phys.veloc.rotat

    sptablerule

F.16 Changes from v0.2

  1. Section 1.2 has been simplified

  2. new syntax codes (E, C, V) have been introduced, and described in appendix A

  3. The following words have been renamed

    New corresponding UCD

    sptablerule

    Deprecated UCD

    em.line.HI

    sptablerule

    em.line.21cm

    instr.ang-res

    instr.angRes

    instr.sky-level

    instr.skyLevel

    instr.sky-temp

    instr.skyTemp

    instr.antenna-temp

    phot.antennaTemp

    phys.absorption.gf

    phys.gauntFactor

    phys.at.einstein

    phys.at.transProb

    phys.at.level

    phys.atmol.level

    phys.dispMeas

    phys.dispMeasure

    phys.distance

    pos.distance

    phys.polarization.rotMeas

    phys.polarization.rotMeasure

    phys.size.area

    phys.area

    pos.ang.separation

    pos.angDistance

    pos.ec

    pos.ecliptic

    pos.ec.lat

    pos.ecliptic.lat

    pos.ec.lon

    pos.ecliptic.lon

    pos.ee

    pos.errorEllipse

    pos.gal

    pos.galactic

    pos.gal.lat

    pos.galactic.lat

    pos.gal.lon

    pos.galactic.lon

    pos.sg

    pos.supergalactic

    pos.sg.lat

    pos.supergalactic.lat

    pos.sg.lon

    pos.supergalactic.lon

    src.class.star-galaxy

    src.class.starGalaxy

    sptablerule

  5. Some words have been removed. The following table summarizes, when relevant, the suggested replacement to be used.

    Deprecated UCD

    New corresponding UCD

    instr.area

    phys.area;instr

    instr.beam-width

    phys.angSize;instr.beam

    meta.table.axis

    phys.size;meta.table

    phot.color.Cous

    phot.color

    phot.color.Gen

    phot.color

    phot.color.Gunn

    phot.color

    phot.color.JHN

    phot.color

    phot.color.STR

    phot.color

    phot.color.STR.c1

    phot.color

    phot.color.STR.b-y

    phot.color

    phot.color.STR.m1

    phot.color

    phys.at.lineBroad

    spect.line.broad

    phys.distance.compon

    pos.distance;pos.cartesian.x (or y, z)

    phys.distance.gc

    pos.distance;pos.galactocentric

    phys.electron.energy

    phys.energy;phys.electron

    phys.extension

    phys.angSize or phys.size

    phys.mass.fraction

    phys.mass;arith.ratio

    phys.polarization.posAng

    pos.posAng;phys.polarization

    pos.ang

    pos.det

    pos.cartesian;instr.det

    pos.eq.dec.arcsec

    pos.eq.ra.minutes

    pos.eq.ra.seconds

    pos.gal.compon

    pos.cartesian;pos.galactic

    pos.pm.dec

    pos.pm;pos.eq.dec

    pos.pm.ra

    pos.pm;pos.eq.ra

    pos.precess.dec

    pos.precess;pos.eq.dec

    pos.precess.ra

    pos.precess;pos.eq.ra

    pos.proj

    pos.sg.compon

    pos.cartesian;pos.supergalactic

    src.orbital.energy

    phys.energy;src.orbital

    src.orbital.separation

    pos.angDistance;src.orbital

    src.orbital.size

    phys.size;src.orbital

    src.separation

    pos.angDistance;src

    src.veloc.compon

    src.veloc;pos.cartesian

    src.veloc.gc

    src.veloc;pos.galactocentric

    src.veloc.geoc

    src.veloc;pos.geocentric

    src.veloc.hc

    src.veloc;pos.heliocentric

F.17 Changes from v0.1

  1. Descriptions of the words were improved.

  2. Designation of commonly used lines have been moved to em.line.*. As a consequence, terms like em.IR.K.Brgamma or spect.index.Hbeta have been removed.

  3. phys.at and phys.mol have been completely reorganized to improve the overall description of this domain. A new branch phys.atmol has been introduced to group concepts shared between phys.at and phys.mol.

  4. The phot.color section was significantly simplified.

  5. Missing nodes of the tree were added (e.g. em.gamma, em.mm, pos.sg).

  6. Creation of new words: em.wavenumber, meta.ucd, stat.error.sys.

  7. Typos were corrected in em.opt.* units and a few other descriptions.