RE: [DM] IBM-DM-031: No need for namespace nodes

Unfortunately, making this change would require an enormous upset in the
way the XSLT semantics are described (where explicit construction of
namespace nodes is very much part of the model, and is needed because we
allow dynamic construction of namespaces).
 
Michael Kay

-----Original Message-----
From: public-qt-comments-request@w3.org
[mailto:public-qt-comments-request@w3.org] On Behalf Of Don Chamberlin
Sent: 11 February 2004 23:25
To: public-qt-comments@w3.org
Subject: [DM] IBM-DM-031: No need for namespace nodes



(IBM-DM-031) The Data Model document lists namespace nodes as one of the
seven kinds of node. But a node is needed only to preserve identity and
to represent a position on an axis. The identity of a namespace node is
never used, and the namespace axis is deprecated in XPath 2.0 and not
supported in XQuery. Neither XPath nor XQuery provides a way to
construct a namespace node independently of an element node. Therefore
there is no reason to retain the concept of a namespace node in XPath
2.0. It should be replaced by the concept of "in-scope namespaces" as a
property of an element node. The term "in-scope namespaces" is already
widely used (13 times in the Data Model document and 10 times in the
Functions and Operators document). We should make "in-scope namespaces"
one of the properties of an element node, supported by two accessors
(get-namespace-uri-for-prefix() and get-in-scope-prefixes(), which are
already documented in Functions and Operators). We should leave it up to
the implementation how to support these accessors. Various strategies
are possible, including storing all the in-scope prefixes in each
element node, or only storing the "new" prefixes that are introduced by
each node (different from its parent). 

Replacing namespace nodes with the existing concept of "in-scope
namespaces" will shorten and simplify the Data Model document, removing
various accessors on namespace nodes which XQuery does not provide any
way to invoke. Implementations that choose to support the (deprecated)
namespace axis can synthesize "namespace nodes" from the "in-scope
namespaces" property of an element node. Implementations that do not
support this deprecated axis need not be aware of namespace nodes at
all. All references to "namespace nodes" in XPath and XQuery-related
documents (such as the Serialization document) can be rephrased in terms
of the more abstract concept of "in-scope namespaces" for an element;
this provides greater implementation flexibility and in many cases
simplifies the documents. 

--Don Chamberlin