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Re: multiply-connected graph of schema import

From: C. M. Sperberg-McQueen <cmsmcq@blackmesatech.com>
Date: Mon, 18 Apr 2011 09:42:04 -0600
Cc: "C. M. Sperberg-McQueen" <cmsmcq@blackmesatech.com>, xmlschema-dev@w3.org
Message-Id: <E318F87D-FD30-4BCD-816A-2B05A13BF725@blackmesatech.com>
To: Paul Harrison <paul.harrison@manchester.ac.uk>

On Apr 18, 2011, at 1:52 AM, Paul Harrison wrote:

> Is a multiply-connected (but non-circular) graph of schema imports allowed by the standard?
> 
> e.g  B imports A
>      C imports B
>      D imports C and A
> 
> 
> The intention is that schema D extends types that appear in schemas C and A. There seems to be some confusion in various tools as to what is needed - it seems that some tools require the explicit import of schema A if D makes an explicit extension of a type in schema A, but other tools will report that the types in A have been defined twice it this explicit import is made.
> 
> I would like a opinion on what should be happening according to the standards, so that I can complain to one of the schema tool writers that I am using.....


For some tools, the result will depend on which schema
document you start with and/or the order in which various
inclusions, imports, or schemaLocation hints occur in the
relevant schema document.

The treatment of schema composition is cloudy enough in
both XSD 1.0 that it's very difficult to make a conclusive 
case for, or against, any particular behavior as being 
clearly required or clearly non-conforming.  And unfortunately
the WG has been too deeply divided to be able to do anything
to clear things up in XSD 1.1.  (When shown an example
in which five different implementations produced eight
different behaviors, depending on how they were invoked,
one WG member seriously argued that it really wasn't an
issue, because the spec does not try to specify any rules for
how command-line invocation is handled.  The chair
ruled, not unreasonably, that there was really no prospect 
of reaching consensus on any change in the rules for
schema composition.)

-- 
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* C. M. Sperberg-McQueen, Black Mesa Technologies LLC
* http://www.blackmesatech.com 
* http://cmsmcq.com/mib                 
* http://balisage.net
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Received on Monday, 18 April 2011 15:42:50 GMT

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