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   Re: [xml-dev] The subsetting has begun

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On Wednesday 26 February 2003 19:18, Cavnar-Johnson, John wrote:
> As fascinating as this is, what does it have to do with subsetting XML?

It rose from discussion of whether XML could have a meaningful common data 
model at all, or if it was only globally a synctic constraint on character 
strings; my argument is that if it is a syntactic constraint on character 
strings at all (meaning, XML can be defined by "the set of all possible 
strings which are well formed XML documents") then, due to the nature of the 
constraints that define that set (well formedness), it's inherently a tree 

Even if you don't *have* to base your processing around the tree structure, 
as SAX doesn't, the tree structure is still there. Likewise, somebody using 
DOM bases their work entirely around the tree structure and ignores the fact 
that it might once have been a linear stream of something.

Then somebody said it was a DAG, which I said it isn't, but then two people 
came up with challenges to this; one saying that he can avoid re-specifying 
duplicated subtrees in instances by putting them into entities and 
referencing them, and another by saying that you can define an otherwise 
non-special type of leaf node to represent a pointer to another part of the 
tree and then state that the resulting relationship is supposed to represent 
identity, but the first is missing the point and the second is just decribing 
a way you could encode a DAG into a tree.

But the overall theme of the subthread is my argument that failing to 
formally specify a data model for XML doesn't prevent there being an inherent 
tree structure due to the structure of the definition of XML, but it doesn't 
make a DAG :-)

Does that about cover it?


A city is like a large, complex, rabbit
 - ARP


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