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   Re: [xml-dev] Still banging on about extensibility and validation

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At 2006-05-04 23:10 +0200, bryan rasmussen wrote:
>>I think ISO/IEC 19757-4 NVDL is the mechanism by which we can safely
>>look at XML instances using the view that sets of labeled information
>>found in a single instance *each have their own model* ... those sets
>>identified unambiguously through the use of namespace-rich
>>labels.  This is not achievable with the traditional view that the
>>entire instance *has a single model* that is sacrosanct.  The real
>>world does not accommodate this traditional view well when trying to
>>accommodate different users' needs.
>I'm actually having some problems with NVDL, because I was having a
>hard time reading in the available documentation how one would handle
>specific common situations.

All in good time ... there is a lot of standardization underway and 
we can't get to all the user documentation.  I do believe the answers 
are in the spec.

>These are:
>1. Namespace qualified attributes on an element of another element.
>I really can't think of any way one could handle that in a reasonable
>manner, and I suspect that in most scenarios this would be one
>namespace extending another, not a mix of two data sets. But I don't
>this for a fact, just a suspicion.

This is accommodated.  NVDL provides for a generic element to which 
the attributes are attached.  A schema expression to validate the 
attributes incorporates the presence of the generic element.  The 
combination gets dispatched for validation.

>2. propogation of text nodes up from elements in namespace y to
>elements in namespace x, example:
><y:y>text node</y:y>
>in this scenario y:y is extending x:x,

But it is distinct.

>and conceptually we assume that they share the text node.

They do not.  In the data model for that fragment, x:x has three 
children: two text nodes of only white-space, and one element node 
being y:y ... the string "text node" is only a child of y:y.

>so when split they should be
><x:x>text node</x:x>
>and <y:y>text node</y:y>

I disagree.  I don't know of any data model for XML in which text 
nodes are "copied" or considered a property of an ancestor.

>I think this is a reasonably common usage but I'm not sure if NVDL
>handles it.  I suppose the argument could be made that this is an
>extremely dangerous and dirty usage, and we would not want to automate
>that kind of splitting of data.

On that I agree ... but since the data model does not "split" the 
data as you describe, it fortunately isn't an issue for NVDL.

I hope this helps.

. . . . . . . . . . Ken

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