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XPath 2.0 - What is a "node"? What is an "item"?

• To: xml-dev@l...
• Subject: XPath 2.0 - What is a "node"? What is an "item"?
• From: AndrewWatt2000@a...
• Date: Mon, 13 May 2002 10:11:07 EDT

[The following was sent a short time ago to the public-qt-comments list. If 
anyone on XML-Dev can clarify my current lack of clarity that would be good.]

I am currently wrestling with what the 30th April Data Model WD. It seems to 
me that there is a fundamental inconsistency in expression relating to what a 
node or information item is, as described in the WD. I hope that the 
difficulty is only in terms of how ideas have been expressed.

In 1. Introduction it is stated that "The data model is based on the 
Information Set". I took that to indicate that XPath 2.0 Data Model 
incorporates all of the Infoset REC.

However, in 4.1 the description of a document node omits several properties 
of the document information item as described in the Infoset REC.

Further, it is stated in 1. that "An item is either a node or an atomic 
value.". I read that to refer to an "information item".

If that is the case then an "information item" is essentially identical to a 
"node".

However an Infoset "information item" has a number of properties which a 
"node" at least as described in XPath 1.0 does not possess. So, it seems that 
an XPath 2.0 node is fundamentally different from an XPath 1.0 node in that 
it now possesses a full set of Infoset properties.

Yet in 4.1 it is stated "Document nodes and XPath 1.0 root nodes are 
essentially identical.".

Yet if an XPath 2.0 document node "is" (as quoted from 1. above) an "item" 
and if an "item" is intended to be the same as an Infoset "information item" 
it is not possible for an XPath 2.0 document node (which must possess Infoset 
properties) to be "essentially identical" to an XPath 1.0 root node (which 
possessed no Infoset properties).

I hope I have conveyed something coherent of what I perceive as the 
inconsistency of descriptions.

My questions now include, What did the WG intend to say about the 
relationships of an XPath 2.0 "node" and an XPath 2.0 "item"? Does an XPath 
2.0 node have (or not have) a full complement of Infoset properties? How, 
precisely, does an XPath 2.0 node differ from an XPath 1.0 node?

Andrew Watt

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