RE: [xml-dev] Backward and forward compatible schemas ... Relax NG -->

["Dave Orchard" <orchard@pacificspirit.com>]

The blanket statement that XML schema 1.0 does not support forwards and backwards compatibility is incorrect.  Using an "Extension"
or "Sentinel" element, one can get around XSD 1.0 UPA constraints at the cost of extra markup in instances.  This is shown in the
W3C TAG Versioning Finding(editors draft) XML and Schema doc, section 7.4 http://www.w3.org/2001/tag/doc/versioning-xml#versionid3
and in the section 4 "Version Strategy" of an XML.com article explaining forwards compatibility using XSD 1.0
(http://www.xml.com/pub/a/2004/10/27/extend.html?page=4)

Cheers,
Dave

> -----Original Message-----
> From: noah_mendelsohn@us.ibm.com [mailto:noah_mendelsohn@us.ibm.com] 
> Sent: Thursday, August 23, 2007 4:45 PM
> To: Costello, Roger L.
> Cc: xml-dev@lists.xml.org
> Subject: Re: [xml-dev] Backward and forward compatible 
> schemas ... Relax NG --> Yes ... XML Schema --> No
> 
> Roger Costello writes:
> 
> > However, the new schema is not legal; an optional element 
> prior to an 
> > <any/> is not legal, as it makes the content of Book 
> > "non-deterministic";
> 
> True in W3C XML Schema 1.0;  not true in the proposed Schema 
> 1.1.  For exactly the reason you describe, I.e. that to make 
> languages extensible one wants to write schemas just like 
> this, Schema 1.1 will change the Unique Particle Attribution 
> constraint, which is the one that enforces the determinism in 
> question here.  In schema 1.1, UPA will be violated only if 
> the same content in some instance could match two or more 
> element particles or two or more wildcard (<xsd:any>) ;  
> particles.  A wildcard "competing" witn an element is OK in 1.1.
> 
> > Do you agree with my assertion: Relax NG supports backward 
> and forward 
> > compatibility
> 
> I'll take your word for that.  Haven't used RNG in enough 
> real scenarios to be sure.
> 
> 
> > but XML Schemas does not?
> 
> Agree for Schema 1.0, disagree for Schema 1.1.
> 
> Noah
> 
> --------------------------------------
> Noah Mendelsohn 
> IBM Corporation
> One Rogers Street
> Cambridge, MA 02142
> 1-617-693-4036
> --------------------------------------
> 
> 
> 
> 
> 
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