Re: [Psidev-ms-dev] Vote on the fate of the version attribute

[Chris A. <ch...@ma...>]

Matthew Chambers wrote:
> As we discussed at least week's call, there's some debate about the 
> value of having a separate version attribute. There seem to be two sides 
> to the debate:

Just out of interest: What's the intention with backwards compatibility 
policy here?  If there are breaking changes to the schema that render 
previous instance documents no longer valid, anyone using a validating 
parser (eg. XercesC, MSXML) will struggle to support reading more than 
one major version without a namespace change since you can only map each 
unique namespace URI to one xsd file^^, and that mapping has to be given 
to the parser _before_ it starts reading the document (chicken and egg). 
  Relying only on a version attribute in the document or the 
"schemaLocation" would require a 2-pass approach, which isn't very 
practical if you're reading the document from a (forward-only) stream.

See also:
http://209.85.229.132/search?q=cache%3AVyWUtbQUsFAJ%3Awww.xfront.com%2FVersioning.pdf+%22XML+Schema+Versioning+Best+Practices%22&hl=en&gl=uk

^^ Yes, instance documents can also provide this mapping (via 
"schemaLocation") but it is only a hint and quite often it's not 
practical to rely on for an application because it is optional and may 
point to a schema location that doesn't exist locally (eg. transferring 
file between platforms) or isn't accessible for some reason.  Usually 
the application will ship with a copy of the schema that it supports and 
it will want to use that instead.

btw, if you choose to encode the full version number in the XSD 
filename, that potentially means the application requires a copy of each 
and every version it will support.  If the changes are backwards 
compatible that seems over the top since the newer version will still 
validate older instance documents.

Regards,
Chris