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UCD Proposed Recommendation.
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Comments
A couple of points from the ESO crew.
UCD version : by MarcoLeoni. It's crucial to be able to distinguish between UCD version. Even more important, services do not have to use differente UCD version in the same document: this should be made clear in the Rec., thus allowing validation of documents using UCDs.
Answer (by IVOA..SebastienDerriere):
The main distinction to do is between UCD1 and UCD1+. All VO services and standards that will be defined after UCD1+ are promoted to an IVOA Recommendation must explicitely refer to the UCD1+ as being the standard to use.
Tools will be provided to ease the transition from UCD1 to UCD1+
The UCD1+ list of words will be under configuration control (this is now said explicitely in the document). A tool is provided to validate UCD1+, and to ensure that they conform to the latest standard list.
It's not only about the transition UCD1→UCD1+: every time a new standard is achieved, you have to take care of software based on one of the previous. For example, it can happen that some piece of software is no longer maintained: suppose that it can accept UCD1+ but the standard is UCD2, how can it handle the input? Having the possibility to check the version, it can says something like "not supported". Otherwise the only thing you get is a stack trace.
Imposing the presence of a semicolon at the end of every UCD was discussed, and it was found too constraining.
Following the original suggestion by AlbertoMicol, it is now required in the document that for any two UCD1+ words at the same level in the hierarchy, one should not be a substring of the other. This will impose a few changes in the current list of words, that the Scientific Board will take care of.
