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Re: Need Union and RE: Should I organize a call on the XPath Filter?

From: Joseph Reagle <reagle@w3.org>
Date: Thu, 21 Mar 2002 17:54:54 -0500
Message-Id: <200203212254.RAA18412@tux.w3.org>
To: "John Boyer" <JBoyer@PureEdge.com>, "merlin" <merlin@baltimore.ie>
Cc: "Christian Geuer-Pollmann" <geuer-pollmann@nue.et-inf.uni-siegen.de>, "TAMURA Kent" <kent@trl.ibm.co.jp>, <w3c-ietf-xmldsig@w3.org>

Ah, I was confused about the distinctions between the "input document" and 
"input nodeset." I've realized we should promintly highlight and define  
the difference between the input nodeset, and the root element of the whole 
tree that still exists in context.

Also, I have a *little* bit of concern in that we're implicitly thinking in 
terms of DOM implementation and the relationship to the whole of the tree 
being preserved when we are handed a nodeset. (If this design is 
unavoidable/desired, perhaps we could make it more explicit?) What happens 
if I had a stream-like implementation of a profile of XPtr or XPath, or 
some weird conversion between an Infoset? XPath defines a node-set as, 
"node-set (an unordered collection of nodes without duplicates)" so there's 
nothing there that guarentees the preservation of relationships with other 
nodes, right?

I don't disagree with the distinction, I'm just not confident we aren't 
relying upon some implicit statement somewhere that the result of one of 
our XPath transforms (or profiled XPtr) MUST preserve its relationships to 
nodes not in the node-set. Perhaps we need to define an "input nodeset" 
"document nodeset" and "evaluated nodeset" and state the relationships 
between the "evaluated nodeset" and "document nodeset" MUST be preserved.

On Wednesday 20 March 2002 13:35, John Boyer wrote:
> <merlin>
> To answer 2, in case it's not clear from my last message (which
> hopefully
> addresses 1), the XPath expression is evaluated in the context of the
> input document and then the result is applied to the input node set.
> </merlin>
> <jb>
> Yes, and I would further assert that the set operation transforms *are*
> operating over the output result of the preceding transform in a natural
> way, esp. given that we want to avoid running lots of XPath expressions.
> An Xpath evaluation context takes one node.  If we want to run the Xpath
> over each node of the input, then use Xpath filter 1.0.  Otherwise, we
> run one Xpath over the document from which the input node-set is drawn,
> then we perform a set operation between the Xpath result and the input
> node-set....
Received on Thursday, 21 March 2002 17:55:05 GMT

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