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RE: Data Model - Inconsistent?

From: Paul Cotton <pcotton@microsoft.com>
Date: Wed, 15 May 2002 19:35:14 -0400
Message-ID: <E7AC4500EAB7A442ABA7521D18814397032F95A4@tor-msg-01.northamerica.corp.microsoft.com>
To: <AndrewWatt2000@aol.com>
Cc: <public-qt-comments@w3.org>, <marton.nagy@saic.com>
I think an Editor of the Data Model may be able to answer your detailed
questions but I wanted to reiterate what I said in a previous reply.  

The text "The data model is based on the Information Set" must not be
read to mean that there is an isomorphic mapping between the Data Model
and the Information Set.  The DM document tells you how to construct a
DM instance from the Infoset (and PSVI).  You should not assume you are
then operating on an Infoset.  Please remember that the Infoset is just
set of terms that describe what an XML parser returns.

/paulc
Chair, XML Query WG

Paul Cotton, Microsoft Canada 
17 Eleanor Drive, Nepean, Ontario K2E 6A3 
Tel: (613) 225-5445 Fax: (425) 936-7329 
<mailto:pcotton@microsoft.com> 


> -----Original Message-----
> From: AndrewWatt2000@aol.com [mailto:AndrewWatt2000@aol.com]
> Sent: Monday, May 13, 2002 10:10 AM
> To: public-qt-comments@w3.org
> Subject: Data Model - Inconsistent?
> 
> 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
Received on Wednesday, 15 May 2002 19:35:38 GMT

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