RE: [xml-dev] XML processor behavior with unused NS declarations

["Jim Tivy" <jimt@bluestream.com>]

Hi Evan

Ideally an Xml processor should not throw away any namespace declarations
reduntant or not since sometimes people hack things into serializations
depending on a yet unused namespace declaration.

The apache serializer - now deprecated had a restriction where there could
only be one prefix declared for a given namespace url, so it dropped
redundant declarations that someone was depending on for some downstream
processing.  I realize you can argue the downstream processing should not
rely on the upstream declaration - but hacks often make things work.

Jim 


-----Original Message-----
From: Evan Lenz [mailto:evan@evanlenz.net] 
Sent: Wednesday, July 22, 2009 2:15 PM
To: Chuck Bearden
Cc: xml-dev@lists.xml.org
Subject: Re: [xml-dev] XML processor behavior with unused NS declarations

Hi Chuck,

Sorry to be late to this thread. It sounds like you've gotten your 
answer already: don't throw the namespace declaration away. If you're 
interested in reading some more discussion/background on the reasons 
why, check out the "QNames in Content" section of a paper/chapter I 
wrote called "Understanding XML Namespaces".[1]

Of course, it's always safe to throw away *redundant* namespace 
declarations when serializing XML, provided you're not just serializing 
a fragment (in which case it wouldn't be redundant anymore). For 
example, if the <h2> element in your example merely repeated the 
xmlns:dc declaration verbatim, it would be safe to leave that out of 
your serialized result. (And Canonical XML *requires* such superfluous 
namespace declarations to be removed.) You just can't make any removals 
that would make a difference to the XPath data model's abstraction of 
your document.

Evan Lenz
Lenz Consulting Group

[1] http://lenzconsulting.com/namespaces/#qnames_in_content
[2] http://www.w3.org/TR/xml-c14n#SuperfluousNSDecl


Chuck Bearden wrote:
> Is a namespace-aware XML processor permitted to drop a namespace 
> declaration when no elements or attributes in that namespace are used 
> within the scope of the declaration?  Say, given this example from the 
> RDRa Primer:
>
>   <div xmlns:dc="http://purl.org/dc/elements/1.1/";>
>      <h2 property="dc:title">The trouble with Bob</h2>
>      <h3 property="dc:creator">Alice</h3>
>      ...
>   </div>
>
> there's no danger of the processor dropping the 'xmlns:dc' 
> declaration, correct?
>
> I looked at the Namespaces in XML recommendation, and it doesn't 
> mention omitting them.  A namespace-unaware processor would treat NS 
> declarations like attributes and hence not drop them, so I reckon that 
> a NS-aware processor should match that behavior as well, but 
> confirmation from the cognoscenti is welcome!
>
> Thanks
> Chuck


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