UCD List 1.3 Proposed Recommendation: Request for Comments

Public discussion page for the UCD List specification version 1.3 Proposed Recommendation

The UCD Standard has defined a vocabulary for classifying physical quantities and labeling dataset descriptions as well as dataset content and has offered a reference list for the values of these semantic labels at http://www.ivoa.net/documents/cover/UCDlist-20070402.html.

It has been revised to include new terms, for statistical quantities, for measurements required by the planetary science and solar physics community, for finer description of metadata.

All new terms have been discussed and checked in their context of use and added to this specification.

New parts of this proposed recommendation compared to the previous version of the UCD List are marked in yellow in this current PR document for easy reading.

The latest version of UCDList is now version 1.3 and can be found on the document repository at http://www.ivoa.net/documents/UCD1+/20170831/index.html

The colored version provided here is easier to spot the added terms and changes .

All changes are in the colored text ( green text, yellow highlighted terms) .

The document has been updated according to the comments addressed during the TCG review .

it is now available as http://wiki.ivoa.net/internal/IVOA/UCDList2017RFC/PR-UCDlist-1.3-20170831-Update20180208.pdf

Latest decisions and updates after UCD maintenance commiteee feedback :


-- MireilleLouys - 2018-02-19

Reference Interoperable Implementations

UCDs are used everywhere in the VO ecosystem, in catalog tables, metadata description, service parameters, etc.

In the VOTable specification, FIELD and PARAM elements have a 'ucd' attribute that should take values into the recommended list of terms provided in this specification.

TAP Schemata also define UCD to qualify their columns.

Implementations Validators

The CDS UCD builder allows to find an appropriate UCD term from a free text description.

It has been revised to support the new terms of the vocabulary.

Check the new version at : http://cds.u-strasbg.fr/UCD/cgi-bin/descr2ucd

Table of Contents

Comments from the IVOA Community during
RFC/TCG review period: 2017-09-06 to 2017-10-06

The comments from the TCG members during the RFC/TCG review should be included in the next section.

In order to add a comment to the document, please edit this page and add your comment to the list below in the format used for the example (include your Wiki Name so that authors can contact you for further information). When the author(s) of the document have considered the comment, they will provide a response after the comment.

Additional discussion about any of the comments or responses can be conducted on the WG mailing list. However, please be sure to enter your initial comments here for full consideration in any future revisions of this document

Comments from TCG member during the RFC/TCG Review Period:
2017-09-06 to 2017-10-06

WG chairs or vice chairs must read the Document, provide comments if any (including on topics not directly linked to the Group matters) or indicate that they have no comment.

IG chairs or vice chairs are also encouraged to do the same, althought their inputs are not compulsory.

TCG Chair & Vice Chair

Applications Working Group

I approve of these changes, but have some suggestions/questions below:

Some the new words have a desription that starts with "Related to". While I know these descriptions are brief and cannot be very specific, the "related to" phrasing seems like it might be too vague. If, for example, meta.ref.doi should be an actual DOI, then the "related to" is too vague. If it can contain values other than actual DOIs, then the "related to" may be OK, but the vagueless of the UCD makes it less useful.

Section 3.2 seemed awkward to me, mostly because it took me a while to realize why it was there. Some suggestions that might make its purpose clearer:

  • The section heading, Combination Rules, looks like the section will define those rules. Although the first sentence says where the rules are defined, it may help to soften the section title with something like, Remarks on Combination Rules
  • The first of the questions might be clearer as, "How do UCDs differ from structured descriptions?"
  • The numbered bullet answering the first question is not needed. It can just be a paragraph.
-- TomDonaldson - 2018-01-30

This has been taken into account in the updatesd PR document. Thanks

"Related to" is now only used when the term is 'S' , which means it is a qualifier of some other UCD which should be a real piece of information e.g meta.title;meta.query , meta.url;meta.preview, etc.

-- MireilleLouys - 2018-02-08

Data Access Layer Working Group

DAL is approving this specification, but make some suggestions or remarks to improve the document.

a ) justify the main text

b ) subtitle = is the Update only for Planetary and solar data ? ---> "Update including new terms for Planetary and solar data"

c ) 2.5 (obs) we don't understand the exact meaning of "In practice the section is "thin"....". Do you mean "housed" under another "first atom" ? We think it's usefull to identify concepts related to an observation process.

d ) 6 phot. replace "measures" by "measurements" according to this "https://english.stackexchange.com/questions/56387/measure-vs-measurement"

d ) 2.8 pos. misses "coordinate systems" ? the second item "Angular mesurements in general. The WCS FITS keywords" with the irst part in green looks odd.

e ) 2.9 spect. Distinction betwwen em and phot is clear. spect looks more as describing the functional dependance of flux wrt spectral coordinate itself (shape, etc...) than the flux axis as it is written. Should be good to modify the sentence a little.

f )3.1 in the list of VO protocols "ObsTAP" should be either "ObsTAP and SIAV2" or "ObsCore".

g ) "Current question" . P and S must be explicited when used for the first time

h ) In the long list we only noticed the lack of time.stop at the very end

-- FrancoisBonnarel - 2018-02-02 -- MarcoMolinaro - 2018-02-02

All suggestion updates applied except h) because time.end exists in the Ucd Tree for this concept already. Thanks.

-- MireilleLouys - 2018-02-08

Data Model Working Group

Apart the fact the orange items are difficult to read, DM agrees

-- LaurentMichel - 2017-11-08

Removed the original orange color for the main nodes of the UCD tree and turned to Bold slanted black font.

-- MireilleLouys - 2018-02-08

Grid & Web Services Working Group

I approve. Just a couple of formatting-related suggestions below:

  • The extra spaces in the author list on the front page should be cleaned up.
  • As Laurent mentions, the orange could be removed.
  • In Appendix B, Changes from previous versions, it is difficult to tell what is new in this document. It is all the entries util Changes from v1.11 (Rec20051231), the previous REC?
-- BrianMajor - 2018-01-31

Document updated accordingly - Thanks

-- MireilleLouys - 2018-02-08

Registry Working Group

(1) I'm rather skeptical about having sect. 3 in here; in particular "current questions" is, I think, inappropriate for a document that has REC status; in addition, this particular document should IMHO only have the role assigned to it in the UCD Maintenance document.

Content-wise, I think the section should go into the UCD standard itself, http://www.ivoa.net/documents/latest/UCD.html -- that's where philosophy and usage of UCDs are discussed.

This has been added in order to allow the user to find the rules together with the list of terms. This helps when people (authors, documentalists, etc.) have to assign a UCD to a column quantity -- MireilleLouys - 2018-02-19

(2) I have reservations about arith.squared; the trouble here is that this changes units, which is something I'd like to avoid with secondary words. I've always considered secondary words as "giving more details" rather than as "changing the fundamental meaning", and the material in the proposed sect. 3 seems to support that. However, the square of a temperature is fundamentally different from a temperature. So, I'd rather say no to arith.squared (I'm mildly negative to arith.sum and arith.variation, but I could live with them). What are the use cases for it?

A squared quantity. It will be upto the user to mention appropriate units. -- MireilleLouys - 2018-02-19

(3) The new meta.* UCD atoms all have descriptions starting with "Related to", which seems wrong at least where these things are Q (rather than S). It would feel much more logical if meta.preview were S and kept its "Related to" (the thing clients would look for then is "meta.ref.url;meta.preview"). meta.query would be a P for me (what would be a use case where it could be S?).

And why are meta.ref and meta.ref.url P, but meta.ref.(doi|ivoid|ivorn|uri) Q? Where would the latter be in an S position where the former couldn't just as well be? [my preference without having seen further use cases: make them all P]

We have been careful when defining the meta subtree as we may not have considered all the possible use-cases for an extended usage yet. Allowing Q seems more careful. However, for all dereferenceable string as mentionned above, we agree this is safe to put all as P.

-- MireilleLouys - 2018-02-19 and 2018-03-05

(4) As a general rule, I'd say anything that can be in P position cannot have a description unconditionally starting with "Related to" -- at least where UCDs are used on columns, I've always understood them to be the second arguments in is-a relationships, as in "raj2000 is-a main value of a right ascension of an equatorial position" for

 <FIELD name="raj2000" ucd="pos.eq.ra;meta.main"> 

-- and you can't say "foo is-a related to...". For S atoms, that's not an issue, of course. Following this, I'm mildly opposed to the "Related to" in front of phys.virial (which is Q). As long as phys.virial remains Q (rather than S), I'd say the "Related to" at least needs to be in parentheses.

Changed to S for phys.virial and phys.atmol.collisional to stick to the "Related to" meaning -- MireilleLouys - 2018-02-19

(5) Why is variance in the description of stat.stdev underlined? Incidentally, the fact that there's stat.variance and stat.stdev (shouldn't this be stat.stddev?) also speaks against arith.squared; with it, stat.stdev;arith.squared would be the same as stat.variance, which seems irregular.

-- MarkusDemleitner - 2017-09-07

Oh, also, I've just stumbled across this (p. 18): "Deprecated: meta.ref.ivorn IVORN are no longer recommended in the VO context and replaced by IVOID. use meta.ref. ivoid instead"

That text is a bit misleading; it's just the term ivorn that's been used inconsistently in the past, the URL community have deprecated URN, and therefore there's no use to keep IVORN in addition to IVOID. So, I'd much rather see the following language: "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"

On the other hand, I'd not be totally opposed to keeping the UCD as it is now and explaining '("ivorn" was historically used for "ivoid"; for backwards compatiblitiy, the UCD literal has been retained)' in the UCD explanation. That's mainly because I'd say if we remove terms or rename terms we're really not in the realm of minor version updates any more, and I'd rather not contribute to such slightly fringy activities.

-- MarkusDemleitner - 2017-10-27

agreed and updated accordingly. Kept meta.ref.ivorn into the list as deprecated

-- MireilleLouys - 2018-02-08

While I'm still fairly unhappy about arith.squared, that shouldn't stand in the way when nobody else has worries about it. So, Registry is ok with moving this onward. -- MarkusDemleitner - 2018-04-18

Semantics Working Group

Document approved , after the revision and updates following comments given during the TCG review.

-- MireilleLouys - 2018-02-19

Data Curation & Preservation Interest Group

Education Interest Group

Knowledge Discovery in Databases Interest Group

Theory Interest Group

Solar System Interest Group

Document approved.

-- BaptisteCecconi - 2018-02-22

Time Domain Interest Group


Standards and Processes Committee

TCG Vote : Vote_start_date - Vote_end_date

If you have minor comments (typos) on the last version of the document please indicate it in the Comments column of the table and post them in the TCG comments section above with the date.

Group Yes No Abstain Comments


Topic attachments
I Attachment History Action Size Date Who Comment
PDFpdf PR-UCDlist-1.3-20170831-Update20180208.pdf r1 manage 529.0 K 2018-02-08 - 21:28 MireilleLouys Update for PR 1.3 after TCG review
Unknown file formatdocx PR-UCDlist-1.3-20170831-colored.docx r1 manage 89.2 K 2017-08-31 - 20:17 MireilleLouys colored version for tracking changes
PDFpdf PR-UCDlist-1.3-20170831-colored.pdf r1 manage 532.7 K 2017-09-01 - 13:51 MireilleLouys colored version for UCD list Update / PR
PDFpdf PR-UCDlist-1.3-20170831.pdf r1 manage 528.3 K 2017-08-31 - 20:10 MireilleLouys Proposed recommendation
PDFpdf PR-UCDlist-1.3-20180219.pdf r1 manage 531.8 K 2018-02-19 - 12:12 MireilleLouys Updates on PR after TCG comments and UCD maintenance committee advice
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Topic revision: r16 - 2018-06-20 - GiuliaIafrate
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