Public Comment

[comment-form@oasis-open.org]

Comment from: dorchard@bea.com

Hello,

I have reviewed the UBL Naming rules, located at http://www.oasis-open.org/committees/download.php/9236/cd-UBL-NDR-1.0.pdf.  As requested, I have sent a comment via the form linked from UBL TC page. 

I have a broad concern that the UBL Naming rules do not allow �compatible evolution� of the UBL components.  In a distributed system, such as the Web and Web services, it is regularly not possible nor necessary to force all parties to upgrade their software at the same time.  There are a variety of strategies that can be used to ensure that a compatible distributed evolution, that is evolution by only 1 side, is possible.  These issues are expanded upon further in the W3C TAG finding on extensibility and versioning [1], an xml.com article on versioning xml vocabularies[2], and an ongoing work on extending and versioning XML languages article [3].  

A design that enables compatible evolution that makes use of XML�s namespace features and supports evolving schemas involves re-using namespace names for compatible, or minor, changes to the names.  This enables namespace aware software to not �break� whenever a compatible change is done.  Should precise identification of the �version� of a vocabulary be required, a version attribute that specifies a �minor� version can be used.  Further, UBL does not enable any extensibility as it does not specify any rules for allowing extensible content models and particularly XML Schema�s wildcard facility and the �Must Ignore Unknowns� rule.  It seems that delivery of the �Universal� Business Language would require 3rd party extensibility, and history has shown that existing formats (like EDI) regularly have extensibility shoe-horned in.

The concepts that UBL naming rules should specify are:
1. The addition of �Must Ignore Unknown� rule, which specifies that consumers of instances that do not recognize content must ignore it and not fault.   This enables forward compatible evolution.
2. NMS2 rule should say �Every UBL-defined or -used schema set MUST have a unique namespace name for incompatible versions�.  The corollary is that compatible versions should use the same namespace name.  Minor nit, namespace names is a better term than �namespace�.  
3. VER5 rule should say �For UBL Minor Version changes, the <name> MUST not change and the namespace name SHOULD not change.
4. If necessary, the VER rules can add that a version attribute can be used to specify a �minor� version of a namespace.
5. The addition of requiring Extensibility in the UBL schemas using Schema�s wildcards.  There are a couple of schema designs that can enable this.
6. Provide a mechanism for 3rd parties to indicate their changes are required, ie incompatible.

These rules, in combination, enable compatible and loosely coupled evolution of the UBL data formats.

Cheers,
Dave Orchard

[1] http://www.xml.com/pub/a/2003/12/03/versioning.html
[2] http://www.w3.org/2001/tag/doc/versioning
[3] http://www.pacificspirit.com/Authoring/Compatibility/ExtendingAndVersioningXMLLanguages.html