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RE: SAX2 Namespace Support

  • From: "Cox Andy" <cox_andy@b...>
  • To: "Leigh Dodds" <ldodds@i...>, "David Megginson" <david@m...>
  • Date: Wed, 5 Jan 2000 11:36:32 -0500

RE: SAX2 Namespace Support
The semantics of operator==() and equals() should match the concept that the
class represents.

If I understand the Namespaces spec [1] correctly, an identical URI (defined
in the spec as "exactly the same character-for-character") and an identical
local part imply an identical QName. According to the spec, "the prefix
functions only as a placeholder for a namespace name." [2]

The URI is the key. Even in the intro, the authors emphasize that the XML
version of namespaces "is not, mathematically speaking, a set."

One man's opinion...

Andy


[1] http://www.w3.org/TR/REC-xml-names/
[2] http://www.w3.org/TR/REC-xml-names/#ns-qualnames

| -----Original Message-----
| From: owner-xml-dev@i... [mailto:owner-xml-dev@i...]On Behalf Of
| Leigh Dodds
| Sent: Wednesday, 05 January 2000 10:47 AM
| To: David Megginson
| Cc: xml-dev
| Subject: RE: SAX2 Namespace Support
|
|
| > In principle (the principle of least surprise), it's very bad
| > behaviour for two objects to be == in C++ or equals() in Java if any
| > of their publicly-accessible fields differ.  Think of sets, for
| > example.
|
| In this instance though your level of surprise is going to relate
| to how familiar you are with the Namespaces spec. After reading
| it I'd be surprised if two QNames with the same URIs and same local
| parts aren't the considered equal.
|
| The problem though boils down to how often, in reality, XML instances
| will have the same Namespace declared twice, with different prefixes.
|
| I'd have thought this would be pretty unlikely. In a data interchange
| context standardising prefixes for Namespaces would mitigate this
| 'problem' and would probably have beneficial side-effects as well.
|
| In a document authoring context I can't imagine using the same
| Namespace with two prefixes, except by accident. Readibility
| (of the XML) is reduced with Namespaces anyway, sprinkling additional
| prefixes around makes this worse.
|
| 2-penneth worth.
|
| L.
|
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