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[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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