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

Evan Lenz wrote:
> 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

Hi Evan,

Thanks for the reply. My question was not about whether my app should throw
away the unused NS declaration, but whether the processors likely to ingest
XML with the RDFa snippet I gave would be likely to (or even permitted to)
throw away the NS declarations for which there are no corresponding elements 
or attributes. The underlying concern was for the robustness of RDFa, and I 
was responding to a question from my project manager.

It seems likely that many RDFa use scenarios would involve NS declarations for
which there would be no attributes or elements in the doc, but whose prefixes
are used as macros for the NS URIs in the RDFa attribute values, e.g.
@property="dc:title" from below, in a doc where no elements or attributes are
in the DC elements NS.

Chuck Bearden (cbearden@rice.edu ; 713.348.3661)
XML Engineer, Connexions

> 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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