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Re: extending schemas...more problems

From: Dan Vint <dvint@mindspring.com>
Date: Wed, 05 Nov 2003 15:31:25 -0800
Message-Id: <>
To: Dean Hiller <dhiller@avaya.com>, xmlschema-dev@w3.org

They may not be mistakes!

The organization may not want their spec to be extended, this is sort of 
like setting block on everything only easier.

I think the bigger problem is what my organization is running into. We want 
to have a standard document instance without specifying which way someone 
might actually choose to extend the standard - and we want to make sure 
that tight validation of element content is possible.

We have come down to 3 methods we are evaluating to extend the spec based 
upon schema techniques:

1) substitution groups
2) derivations
3) redefine

We have different people that like each of these approaches. The problem is 
that depending upon which method I use, the resulting data stream is 
different. Method 1 ends up having a namespace prefix on the containing 
element, Method 2 requires the use of xsi:type and method 3 ends up with 
just the new elements having a prefix.

Because of this situation we will have to define a "standard" extension 
mechanism and setup our schemas according to that preferred method. This 
has already caused weeks of debate and 100's of email trying to decide the 
method to use.

Now add the problem that we want to allow restriction (redefine is the only 
method that supports this) and we have a need to extend and restrict 
enumerated code list data types and we have a real mess.


At 04:00 PM 11/5/2003 -0700, Dean Hiller wrote:

>uh-oh, I ran into another problem with extending schemas.  The standards 
>committee created an element
><xsd:element name="Car"/>
>.....complexcontent here
>Now I can't extend this with extensions and make a CompanyXTypeCar to put 
>more data in for the features we have that are not yet handled in the 
>standard.  This keeps happening over and over every time I go to a new 
>standards.  Is there any was we can get the w3c to change this so elements 
>are extendable too so it becomes impossible for standards bodies to make 
>these mistakes????
Received on Wednesday, 5 November 2003 18:30:44 UTC

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