Re: [XML Schema 1.1] Is the Conditional Inclusion (VC) stuff useful today?

On 30 Apr 2009, at 09:53 , Costello, Roger L. wrote:

>
> Hi Folks,
>
> I'm having a hard time seeing the usefulness of vc:typeAvailable,  
> vc:typeUnavailable, vc:facetAvailable, vc:facetUnavailable,  
> vc:minVersion, and vc:maxVersion.
>
> I can see its usefulness in future versions of XML Schema (version  
> 1.2, 1.3. etc) but I can't see its usefulness today.
>
> Does it have any usefulness today? If so, can you give me a  
> practical example please?

As Michael Kay has pointed out, existing 1.0 processors can add
support for the vc:* namespace without becoming non-conforming on
that account.  Users of 1.0 processors which don't support the vc:*
namespace can easily pre-process a schema document that uses
the vc attributes into a 1.0-conforming schema document (effectively
using XSLT or some other XML process as a preprocessor for their
1.0 schema processor).

But you are also right that a significant part of the value
of the vc namespace today is that it will make it easier to
specify later versions of XSD with less time-consuming agitation
over issues of syntactic and semantic compatibility.  For anyone
frustrated with the length of time the preparation of 1.1 has
taken, and with the limits the WG has imposed on 1.1 in the
service of backward compatibility, that promise of future
utility is a real present benefit, without which I believe some
members of the WG would have declined to continue work on 1.1.
(YMMV of course.)

-- 
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* C. M. Sperberg-McQueen, Black Mesa Technologies LLC
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