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   Re: Namespace Comments (and dtd encoding)

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  • From: "David G. Durand" <dgd@cs.bu.edu>
  • To: xml-dev@ic.ac.uk
  • Date: Thu, 6 Aug 1998 14:16:49 -0700

At 10:10 AM -0000 8/6/98, Ron Bourret wrote:
>David Durand writes:
>> ><!DOCTYPE A [
>> ><!ELEMENT foo:A (B)>
>> ><!ELEMENT B (#PCDATA, foo:A)*>
>> ><!ATTLIST A xmlns:foo CDATA #IMPLIED>
>> ><!ATTLIST B xmlns:foo CDATA #IMPLIED>
>> >]>
>> ><foo:A xmlns:foo="[first URI]">
>> >   <B xmlns:foo="[second URI]">
>> >      <foo:A>
>> >         <B>asdf</B>
>> >      </foo:A>
>> >   </B>
>> ></foo:A>
>> >
>> The document you give seems legal to me, although I'm not sure about the
>> use of #IMPLIED -- what is the status of the value of the xmlns attribute
>> of the second foo:A, given that there's no value in the instance, and no
>> default or fixed value?
>I believe it is legal, which was my whole point.  Granted, it's a matter of
>aesthetics, but I don't like the idea that such abusive constructions are

I don't see why it's abusive, since it has a clear meaning, that can be
read right out of the instance. I can't think of a reason that you'd want
to do that, but it doesn't seem pernicious. Certainly re-declaring a
namespace prefix inside a context where it's already declared is
potentially confusing, and a good example of why using namespaces can
confuse validation, but it doesn't seem worse than lots of others that
exist whenever namespaces are in use.

>As far as I know, the xmlns attribute is inherited -- this is certainly
>by the first example in section 5 of the namespace spec.  (Murata Makoto also
>implies in a separate message that the prefix is not inherited.  Why?)  I
>assume that is what you are showing in the following example, although I
>understand how it is really different from mine.  The value of foo is still
>inherited by the second foo:A -- this should be unaffected by the presence
>of a

Now that I think about it, your version seems just fine. Indeed only for a
#IMPLIED attribute does inheritance make a lot of sense. Just chock the
question up to my being dense when I posted. It probably reflects my
DTD-based view of the world, where you just use default or #FIXED values to
explicitly put attributes where you want them. If you care about the
details of how I was being stupid, read the next paragraph.

It's a null-value problem. I was asking a question here, because I didn't
know the answer. Many parsers treat #IMPLIED values as a special kind of
value (the "not-specified" value). I was wondering if we have clear
langauge in the standard about inheritance and #IMPLIED values.

>(As an aside, the first element in the resulting tree is A, not B -- a typo.
>Also, B is not prefixed, so it is in the global namespace, not the second
>namespace.  The lack of a prefix places it in the default namespace.
>Since that
>has not been declared, the global namespace is used.)

Completely right. Charles Frankston also noted one of these typos.

   -- David

David Durand              dgd@cs.bu.edu  \  david@dynamicDiagrams.com
Boston University Computer Science        \  Sr. Analyst
http://www.cs.bu.edu/students/grads/dgd/   \  Dynamic Diagrams
--------------------------------------------\  http://www.dynamicDiagrams.com/
MAPA: mapping for the WWW                    \__________________________

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