xml-dev - Re: SAX2: Namespace Processing and NSUtils helper class

[David Brownell <david-b@pacbell.net>]

james anderson wrote:
> 
> hmm..., the thread is becoming rather tenuous, but, if you concur, that
> {"","a",""}, which is descibes <... xmlns="" ... > is not the same as {
> undeclared, "a", valid-prefix }, then how does the notion of nonconformance
> enter into the question re
> 
> > > > {"", "a", ""} == {"", "a", "html"}
> 
> ?

Tim pointed out the spec only allows a null URI in the case of the
default namespace declaration:  xmlns="".  Prefix declarations may
not have a null URI:  xmlns:html="" is someone's bad.  Likewise is
a reference to an undeclared "html" prefix.

At the moment I won't suggest how to expose the former error, but
I'd thought it was pretty clear how to expose the latter.

- Dave


> David Brownell wrote:
> >
> > james anderson wrote:
> > >
> > > i had understood
> > >   {"","a",""},
> > > from the example, to denote a name in a namespace for which there would have
> > > been a declaration, namely a binding such as
> > >
> > >   <... xmlns="" ... >
> > >
> > > for the ignominious "null" namespace. how does this come to correspond to
> > >
> > >   { undeclared, "a", valid-prefix } ?
> >
> > It doesn't.  Namespace URIs clearly have three kinds of values, not that
> > it's specified in the namespace spec very clearly (and I suspect DOM L2
> > may need tweaking to get this right):
> >
> >         - Undeclared (null?)
> >         - Declared as no-value (empty string, "")
> >         - Some URI (the case folk focus on).
> 
> don't they have four?
>           - Undeclared (not "null"; that term already has a different meaning
> in the REC)
>           - Declared as "no namespace":      xmlns=""
>           - Declares as the empty string:    xmlns:html=""
>           - Some URI (the case folk focus on).
> 
> >
> > The distinction between "undefined" and "empty" will be familiar to folk
> > in the database world (maybe with different terms).  SAX2 will have to be
> > clear on how it exposes this.
> >
> > One more edge case for applications to trip over!
> >
> > - Dave
> >
> > > i agree that an "==" implementation needs to account for this, but didn't
> > > think it was nonconformant.
> > >
> > > David Brownell wrote:
> > > >
> > > > David Megginson wrote:
> > > > >
> > > > > Clark C. Evans writes:
> > > > >
> > > > >  > On Sun, 26 Dec 1999 uche.ogbuji@fourthought.com wrote:
> > > > >  > >
> > > > >  > > {"http://www.w3.org/1999/xhtml", "a", ""} ==
> > > > >  > > {"http://www.w3.org/1999/xhtml", "a", "html"}.
> > > > >  >
> > > > >  >          {"","a",""} != {"","a","html"}
> > > > >
> > > > > As I understood it, the suggestion was that
> > > > >
> > > > >   {"", "a", ""} == {"", "a", "html"}
> > > >
> > > > Actually I think the namespace spec defines
> > > >
> > > >     { undeclared, "a", valid-prefix }
> > > >
> > > > as "namespace-nonconformant", AKA some kind of error which they
> > > > neglected to describe well enough to support portable APIs.
> > > >
> > > > Meaning that any application choosing to use such a "Name"
> > > > class (which IMHO is a fine notion) needs to treat this value
> > > > with care ... IEEE floating point math has a variety of sorts
> > > > of "NaN" values, perhaps useful models can be found there.
> > > > I'd suggest that most "==" tests against such a Name ought to
> > > > fail, and ordering tests should cause exceptions.
> > > >
> > >
> 
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