And adding to this point, Ken mentioned earlier that the processing of
an instance could 'strip  off' information items that it isn't
prepared/able to process. Whilst a this can work in the request phase
of a message exchange, what about the response. Imagine a v2 XML
instance arrives at a v1 processor. The processor removes all the v2
stuff it doesn't understand, does its work and then constructs the
response. But the caller is expecting a v2 response and it contains
information items which the v1 application doesn't have, and it may
well want some of the information items that were passed in on the v2
request which were discarded as well.

On the later point, David Orchard, sometimes refers to the ability of
a process to ignore data it doesn't understand as the 'must ignore
pattern'. But there are 2 flavours of this, 'must ignore retain' and
'must ignore discard'.

And since Ken introduced the idea, there might also need to be a
'retain' step prior to any removal of data for legal, regulatory and
sometimes business audit / non repudiation reasons.

Following the debate that an earlier poster referred to, also
mentioned the use of a validator, and the meaning was not necessarilly
meaning XML schema validation. In many circumstances both XSD itself
and validation against XSD is just too brittle.

Fraser.

2009/4/23 Andrew Welch <andrew.j.welch@g...>:
>>> How does the
>>> receiver determine the appropriate schema when the version is not
>>> explicitly referenced?
>>
>> Why not "try one and if it fails try the other"?
>
> There is a problem with this - the document is a v2 doc but fails for
> some reason, so validation falls back to the v1 schema, which also
> fails... which error message gets presented to the user?
>
> You want the v2 failure message, but the system can't confidently give you that.
>
>
>
>
> --
> Andrew Welch
> http://andrewjwelch.com
> Kernow: http://kernowforsaxon.sf.net/
>
> _______________________________________________________________________
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