XML Schema Versioning Policies: Endorsed Note - Request for TCG Comments and Approvals

Document Link: XML Schema Versioning Policies

Comments from TCG members

WG chairs or vice chairs must read the Note, provide comments if any and formally indicate if they approve or do not approve of the Note. IG chairs or vice chairs are also encouraged to do the same, although their inputs are not compulsory.

TCG Chair & Vice Chair ( _Matthew Graham, Pat Dowler )

Applications Working Group ( _Pierre Fernique, Tom Donaldson )

I totally approve the purpose of this note. It is a pragmatic approach for improving the interoperability without breaking the necessary protocol validation level. It is perfectly adapted to the IVOA context.

I have one point to precise before approving it formally : Is it really the responsability of the TCG to decide if a standard evolution requires just a minor update mechanism, or more ? (section 2.1.1). I suppose that the authors of a standard evolution are certainly more able to know if the backward compatibility is, or is not guarantee. The TCG should just check the proposal.

And a suggestion: the syntax of the minor and major number version should be probably explained somewhere at the begining of the document.

-- PierreFernique - 2016-04-25

Data Access Layer Working Group ( François Bonnarel, Marco Molinaro )

Data Model Working Group ( _Mark Cresitello-Dittmar, Laurent Michel )

The approach seems very sensible and appropriate for the IVOA.

Opinions on other comments:

+ about TCG role (2.1.1). I agree that it should be careful about the role of the TCG in determining the version. For backward compatibility items, this should be straight forward and responsibility is on the author side. For errata issues, it seems more likely that the effects will be cross group.. a minor change from the DM perspective, may have larger repercussions on the Registry.. so more TCG involvment may be needed.

+ section 2 intro: I found the wording of the fist sentence confusing.. (not equivalent if only difference is the namespace declaration).. seemed like a typo. I needed the rest to clarify the intent. I think there is purpose to the paragraph, but I think the phrasing could be improved. Also, the case described, would only be true if there were no new 'optional' elements added in the instance.

+ section 2.2.1: "root elements must have a version attribute". I'm not too familiar with the details there.. but. Adding a 'must', would invalidate current responses which don't include it, so this may have to be a 'strongly encouraged' type of thing. I'm not sure I understand Marcus' comments about the root element, but specifying where to find this information seems like a good thing. If not on the root element.. where?

Other extremely minor items:

+ section 2.2: has a double 'the'.. "it becomes imperative that the the minor"

+ since the 'official' schema will be associated only with REC standards, I'd prefer the example 'version' texts be for RECs, not PR or WD.

-- MarkCresitelloDittmar - 2016-05-02

Grid & Web Services Working Group ( Brian Major, Giuliano Taffoni )

Registry Working Group ( _Markus Demleitner, Theresa Dower )

(1) I'm not sure I like the language of

We can use the observation that simply removing the namespace definition from both instances would make the instances both textually the same and equivalent in the strict XML sense to inform the class of changes can be to the schema definition without necessarily needing to change the namespace, and how a client should treat such changes.

(introduction to section 2). I have an uncanny feeling that I don't understand what this is intended to mean. Also, it may be confusing in this context, even more so since

  <doc xmlns="http://example.com/ns"/>

and

  <ns:doc xmlns:ns="http://example.com/ns"/>

indeed are equivalent.

Plus, I think we should not even suggest removing the namespace declarations might be a good idea under any circumstances, as doing this is certain to cause major interoperability problems as soon as the resulting tree is serialised again. I'd vote to remove the entire introductory paragraph to section 2.

(2) In

Hence, in service responses, root elements must have a \xmlel{version} attribute exactly giving the value of the corresponding XSD file's \xmlel{version} attribute.

I'm doubtful of the must. Ok, it is limited to "service responses", but that's a term not clearly defined. In VOResource, for instance, I don't think vr:Resource/@version is terribly useful; worse, the root element of actual responses of OAI-PMH-services is a container element we don't even control. And VOResource doesn't have global elements in the first place. So, I'm much rather have language like:

For such applications, protocols should place \xmlel{version} attributes, typically on the root element(s) of the schema. Their values exactly correspond to the value of the \xmlel{version} attribute on the \xmlel{xs:schema} (i.e., root) element of the XML schema file against which a given piece of software was implemented.

And then we could strike the sentence "When the discovery of ... may be left out" further down.

(3) I think the global exposition would profit if we first discuss xs.schema/@version (current sect 2.2.2) and only then talk about @version in instance documents -- since the schema file is the source of the version string, that seems a bit more logical.

(4) While I personally am a big fan of the plural "schemata", I feel obliged to mention that if we wrote "schema files" instead, we'd probably be subscribing to less controversial terminology.

None of the above points is really serious, though, so regardless of how they are eventually decided, I approve of this document.

Semantics Working Group ( _Mireille Louys, Alberto Accomazzi )

Education Interest Group ( _Massimo Ramella, Sudhanshu Barway )

Time Domain Interest Group ( _John Swinbank, Mike Fitzpatrick )

Data Curation & Preservation Interest Group ( Françoise Genova )

Operations Interest Group ( _Tom McGlynn, Mark Taylor )

Knowledge Discovery in Databases Interest Group ( George Djorgovski )

Theory Interest Group ( _Franck Le Petit, Carlos Rodrigo )

---+++ Standards and Processes Committee ( Françoise Genova)


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