Re: RE: Namespace use cases

On Thu, 9 Jul 2009 17:59:56 -0700, Jim Tivy wrote:
> I would love to hear of some success or horror stories of multi-namespaces
> in authoring content.  Anyone out there doing this in DITA, DocBook, open
> office...
>
> What ever happened to the compound document?

Web services are an obvious use case.  It's true that SOAP is
execrable, but the 'simplest subset' continues to drive it: there's an
"envelope" namespace, which indicates 'this is a message conforming to
certain expectations' (that breaks down when you add in the headers and
the ws-* interoperability mess; perhaps that's a namespaces
counterexample?), and the content is in some other namespace.  That
namespace defines its own rules.  You can't create a "carrier"
namespace without the ability to say something about the content
carried; HTML5 is a rather brilliant example of how limited such
content would be if Powers That Be had to approve every message dialect.

Several XML dialects are designed for inclusion in other dialects--SVG,
MathML are obvious ones.  XPath is an interesting case: it's not an XML
dialect, but does need to be able to navigate arbitrary dialects.
Compare the rigidity and complexity of CSS selectors for a
counterexample.  If XML namespaces weren't such a horrible muddle,
there would probably be more such dialects (and less resistance from,
for instance, HTML proponents, to adopting the technique).

"Microformats" are an example where namespaces would be valuable, but
since microformats are typically HTML-based, instead the designers are
typically forced to contort a limited set of elements and attributes
into unnatural shapes to carry the message.  Sure, you and I can agree
that "<abbr class="key 42">moltuae</abbr> is an encoding for the
meaning of life, the universe, and everything, but it's ... somewhat
non-obvious, shall we say.  Providing a means of extensibility would
enable, in HTML 5, microformats (which are probably not intended for
display in the browser, but which are nonetheless valuable to their
intended users).

On a side note ... someone, I think it was Jim Tivy, suggested in an
earlier message that attributes ought to be in the default namespace.
I would suggest that that's not a good idea.  If you think of
attributes as having a "namespace" scoped by their containing element,
things are a lot more clear.

The "no-namespace" or "global" namespace (xmlns="") is where elements
live if they're not assigned to a namespace.  It should be obvious that
if you have multiple dialects from different authorities competing for
names in that namespace, you're going to lose, probably quickly.  The
same is not true of attributes; attributes in "no namespace" are scoped
by their parent element--a single authority.

<p class="important">Blah</p> current state, html as default namespace
<html:p class="important>Blah</p> current state, xmlns:html=html
namespace
<html:p html:class="important">Blah</p> proposed change.  take
attributes out of their parent's namespace and into the default
namespace, and *every* *attribute* of every element in a non-default
namespace now has to be prefixed, even though it's governed by the same
authority that defined the default namespace.

The scoping of attributes to their container elements is often
confusing to people new to XML, but it is, in my opinion, the right
decision (given the verbosity that would otherwise be introduced).

As they stand, namespaces in XML are awkward and clumsy (needlessly so,
as others have already pointed out, using for example the Java package
style technique for establishing a namespace authority, which is fully
as general as the URIs-that-aren't-really-URIs defined by the
namespaces spec), but not broken ... until you encounter prefixes in
content, at which point ... it's broken.  Is it broken because of
namespaces, or because of namespace prefixes in content?  Well, given
the choice of (uselessly verbose and special-character-studded) URIs as
the namespace identifier, it's hard to demand that they be replicated;
lots of folks are willing to complain about the replication of the
prefix "aliases" anyway.  Clark notation, after all, would solve the
problem ... but hasn't been widely adopted, and I think for exactly
that reason.

Amy!
--
Amelia A. Lewis                    amyzing {at} http://talsever.com
"How does one hate a country, or love one? ... What is love of one's
country; is it hate of one's uncountry? Then it's not a good thing. Is
it simply self-love? That's a good thing, but one mustn't make a virtue
of it, or a profession."
               -- Therem Harth rem ir Estraven

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