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RE: Data Model - Inconsistent?

From: Kay, Michael <Michael.Kay@softwareag.com>
Date: Thu, 16 May 2002 07:56:22 +0200
Message-ID: <DFF2AC9E3583D511A21F0008C7E6210602679DAA@daemsg02.software-ag.de>
To: AndrewWatt2000@aol.com, public-qt-comments@w3.org
> 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.

The model is based on the InfoSet, but it doesn't necessarily include
everything that's in the InfoSet.
> 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".

No, the term "item" used in the XPath data model is quite unrelated to the
term "information item" as used in the InfoSet. We probably need to make
this clearer!
> If that is the case then an "information item" is essentially 
> identical to a "node".

Yes, a node in the XPath model and an "information item" in the InfoSet
correspond pretty closely.
> 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.

No, XPath 2.0 nodes are essentially the same as XPath 1.0 nodes which are
essentially the same as InfoSet information items (though XPath 1.0 was
published before the InfoSet).
> Yet in 4.1 it is stated "Document nodes and XPath 1.0 root nodes are 
> essentially identical.".
Indeed they are.
> 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"? 

The result of an XPath 2.0 expression is a sequence of zero or more items.
Each item is either a node or an atomic-value. A node is, for example, an
element node or an attribute node. An atomic-value is, for example, a string
or a number. 

I hope that makes it clearer.

Michael Kay
Received on Thursday, 16 May 2002 01:56:31 UTC

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