[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: Will XML Schema 1.1 get traction?
At 2012-08-14 16:11 +0100, Andrew Welch wrote: >On 14 August 2012 15:57, John Cowan <cowan@mercury.ccil.org> wrote: > > Rick Jelliffe scripsit: > > > >> I have reached the stage where I think every enumerated list in an XSD > >> (or RELAX NG, or DTD) should be regarded as guilty until proven > >> useful, unless they are stable and unlikely to change in the lifetime > >> of a schema. > > > > I agree in principle. However, such constructs may be not so much a > > schema smell as an organizational smell. Excluding lists from schemas > > presumes that someone else is in the business of making and validating > > them > >I don't really see a problem with holding the enumerations in a file >of their own and versioning them separately to the main xsd. That's >no different to external code lists, and it avoids the separate >additional validation step. The OASIS Universal Business Language TC ended up deciding there was a difference between embedding code lists and externalizing them. Sadly, UBL 2.0 ended up with a hybrid of embedded (from UN/CEFACT schemas) and externalized (from UBL TC schemas) code lists and from version 2.1 all are now external. The OASIS Code List Representation TC published Tony Coates's genericode specification and my context/value association specification as the combination used to create the separate additional validation step you cite. Users use these to create expressions of their code list requirements, and a process creates the runtime artefacts for validation. These specifications are not reserved for UBL, as they work with any XML vocabulary. They are based on XDM and XPath, not on XSD. In UBL, the XSD expressions are normative and the second-pass value-validation expressions are not normative. Every trading partner community, or even a single trading partner relationship, may have differing value-validation requirements, but the UBL XSD expressions are fixed. The real-world scenario that finally demonstrated the problem with UBL 2.0 having embedded the UN/CEFACT currency code list is that Turkey changed their currency symbol a couple years after it was published. Users with that requirement cannot use UBL 2.0 unchanged. UBL 2.1 (and future versions) schemas handle this change and future changes in value validation by recognizing the structural and lexical constraints on a UBL document are inviolate, while the value constraints are likely to be very fluid in a business context (and likely others as well). I have heard the argument that those XSD files with code lists can be managed separately from those XSD files with structure and lexical constraints, but that doesn't address (from a standards committee perspective) that "the published normative schemas are standardized". Anyone claiming that their instance is UBL-conformant (regardless of their value constraints and their imposed subsetting of the UBL optional stuff and their imposed extensions at the standardized extension point) can always have their claim validated by going to the committee repository and downloading the schemas and use them unchanged without any validation errors. They won't be able to do that if XSD 1.1 is used to express enumerations and other value constraints that are fluid for users. Whether XSD 1.1 is needed otherwise for structural and lexical constraints remains to be seen, but I don't think there are requirements yet expressed that require us to explore that now. XSD 1.0 seems expressive enough for the simple relationships that exist from having used ISO/IEC 15000-5 Core Component Technical Specification as the modeling methodology. I hope this helps. . . . . . . . . . . . . Ken -- Public XSLT, XSL-FO, UBL and code list classes in Europe -- Oct 2012 Contact us for world-wide XML consulting and instructor-led training Free 5-hour lecture: http://www.CraneSoftwrights.com/links/udemy.htm Crane Softwrights Ltd. http://www.CraneSoftwrights.com/x/ G. Ken Holman mailto:gkholman@CraneSoftwrights.com Google+ profile: https://plus.google.com/116832879756988317389/about Legal business disclaimers: http://www.CraneSoftwrights.com/legal
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