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Very excited to see this. Is there an all global way to do this or a way to create a reusable library schema set preserving such forward and backward compatibility - something which might be desirable for typical cases needing such versioning? I guess any use of imports might make it less straightforward but does XML Schema 1.1 help with such like? Many thanks -- Stephen Green Partner SystML, http://www.systml.co.uk Tel: +44 (0) 117 9541606 http://www.biblegateway.com/passage/?search=matthew+22:37 .. and voice On 24/08/07, Dave Orchard <orchard@p...> wrote: > > -----Original Message----- > > From: Costello, Roger L. [mailto:costello@m...] > > Sent: Friday, August 24, 2007 8:32 AM > > To: xml-dev@l... > > Subject: [Summary] Backward and forward compatible > > schemas ... Relax NG --> Yes ... XML Schema -->Yes > > > > > > Thanks everyone for your excellent comments! > > > > Special thanks to David Orchard. David, I read your article. > > I now understand how to implement backward and forward > > compatible schemas using XML Schema. The technique you > > illustrate is very powerful. > > Not a problem! And with Schema 1.1, it is much easier to do backward and forward compatible schemas.. > > > Notice that successive schema versions "added" new elements. > > Is there a way for successive versions to remove elements and > > still remain backward and forward compatible? > > > > It depends what you mean by "remove". > > If you mean remove and not accept, then the options depend upon the cardinality in V1. If you mean remove the definition but still > accept, then in general the language can still be fully compatible. An example of remove and still allow would be to replace an > element with a wildcard that allows that element. As we've previously said, this is possible only in some specific cases in XSD 1.0 > - such as an element in a non-targetnamespace being replaced by an any with namespace="##other" - and more generally allowable in > XSD 1.1. The theory is that you've reduced the "defined text set" size but not the "accept text" set, which is forwards and > backwards compatible change. See a formal model of compatibility at > http://www.xml.com/pub/a/2006/12/20/a-theory-of-compatible-versions.html and the TAG versioning finding terminology > (http://www.w3.org/2001/tag/doc/versioning) for more explanation of the terms and set theory. > > Under remove and not accept, elements with maxOccurs greater than minOccurs can have maxOccurs reduced to the minOccurs and the > newer language is forwards compatible because an "newer" producer will then not produce the content up to the old maxOccurs. In the > easy case, this means removing optional content is forwards compatible. The newer language is not fully backwards compatible > because an "older" producer may produce the content with cardinality greater than the new "maxOccurs". If the "older" producer only > produces content within the new maxOccurs, then the producer has effectively subsetted the language such that the language it is > using is backwards compatible. This is one advantage of "partial understanding". > > It is not possible to reduce the maxOccurs less than the previous minOccurs (ie removing mandatory elements) and be forwards > compatible because older consumers will not accept the newer documents because there aren't enough of the element or backwards > compatible because newer consumers will not accept the older documents because there are too many of the element. > > In a more formal model, it is forwards incompatible because Defined Text set of the new language is smaller than the older languages > Defined Text Set (not enough) and it is backwards incompatible because the Defined Text set of the old language is larger than the > Accept Text Set (too many) of the newer language. > > Cheers, > Dave > > > > _______________________________________________________________________ > > XML-DEV is a publicly archived, unmoderated list hosted by OASIS > to support XML implementation and development. To minimize > spam in the archives, you must subscribe before posting. > > [Un]Subscribe/change address: http://www.oasis-open.org/mlmanage/ > Or unsubscribe: xml-dev-unsubscribe@l... > subscribe: xml-dev-subscribe@l... > List archive: http://lists.xml.org/archives/xml-dev/ > List Guidelines: http://www.oasis-open.org/maillists/guidelines.php > >
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