Re: Namespace: what's the correct usage?

[Martin Gudgin <marting@develop.com>]

----- Original Message -----
From: "Simon St.Laurent" <simonstl@simonstl.com>
To: "Martin Gudgin" <marting@develop.com>
Cc: <xml-dev@lists.xml.org>
Sent: Sunday, May 20, 2001 10:32 AM
Subject: Re: Namespace: what's the correct usage?


> On 20 May 2001 07:19:00 +0100, Martin Gudgin wrote:
> > So what would you do with the following XML document?
> >
> > <p:book xmlns:p='urn:x1'>
> >   <p:title>The Hobbit</p:title>
> >   <p:genre>Fantasy</p:genre>
> >   <p:author>
> >     <p:title>Dr</p:title>
> >     <p:familyName>Tolkien</p:familyName>
> >   </p:author>
> > </p:book>
> >
> > All the elements are namespace qualified. How do you distinguish between
the
> > two title elements?
>
> The simple answer is to manage my own name conflicts, and not use
> p:title twice with different meanings.
>
> This would seem (to me) especially obvious in the context of XML Schema
> where type is everything - the only reason this example works is that
> p:title is just simple text.  If the two titles were of genuinely
> different types, there's be a much larger problem.
>
> RELAX provides for this by permitting context-dependent content models,
> but I don't think the RELAX documents encourage the practice you're
> proposing.
>
> > Or take XSLT. xsl:param can appear in two places; as a child of
> > stylesheet/transform or as a child of template. It *does not* mean
exactly
> > the same thing in both places. When it's a child of template the
parameter
> > is local to that template, when it is a child of stylesheet/transform
the
> > parameter is global. How does an XSLT processor distinguish between
these
> > two cases? It treats xsl:param as locally scoped and checks the parent.
>
> Context-dependency matters in a large number of XML use cases. The
> particular kind of context-dependency you are proposing (unqualified
> elements belonging to their parent context) is not supported by the
> Namespaces spec itself, and I think you're making enormous assumptions
> about the kind of processing required to handle them without considering
> the impact on exchange with other users who will not make those same
> unsupported assumptions.

Then why did one of the editors of the Namespace rec use this approach in
SOAP?

>
>
> > I think my argument is that local scoping may well be in effect
*anyway*.
> > People are already using it without realising it. I think that making
> > locally scoped elements unqualified acts as a trigger saying 'look at my
> > parent! look at my parent!'.
>
> But Namespaces in XML already defines scoping explicitly, and says "look
> at my parent for xmlns declarations!" not "look at my parent for its
> namespace URI!"
>
> > I am sharing them in the markup. If the following document appeared at
your
> > door one night, what would you do?
> >
> > <p:person xmlns:p='urn:x2' xmlns='' >
> >   <name>Martin</name>
> >   <age>33</age>
> > </p:person>
>
> I'd wonder why Martin Gudgin was sending me documents which seem to
> demonstrate a serious lack of understanding about namespaces, even
> though he appears to be three years older than I am.  As a human, I'm
> happy to read past namespace declarations and take guesses.  Most
> programs aren't nearly so forgiving.

:-)

I think I understand namespaces reasonably well ( although my understanding
of URN syntax obviously leaves a lot to be desired ). I'm just interested in
exploring this particular approach because it is what SOAP uses and
therefore is being used by a lot of people. I think that in the SOAP world
if a piece of software didn't recognise the qualified person element then it
would not process the message.

>
> > You'd take one look at the namespace name and local-name of the document
> > element and tell it to get lost because you didn't know how to process
it.
>
> No, not necessarily.  I'd look for a RDDL document at the URI specified
> for p, and realize that the sender likes perverse URNs in addition to
> bizarre usage of elements with no namespace URI.

But software is not yet at a stage of being able to read, understand and
generate more software from RDDL.

>
> If you'd dropped a RDDL document at the URI with some kind of
> explanation of what you were up to, I might have used kinder words than
> bizarre and perverse and maybe written some code to cope with your
> usage.
>
> > So, I'm curious, what do you do now if you see an element in no
namespace?
>
> I assume that they were created by people using vocabularies which have
> no namespaces.  A _lot_ of people use XML without using namespaces _at
> all_.

Right! And again, if you were a piece of software you'd stop right there.
But if you'd seen a namespace qualified parent then maybe you'd be fine?

>
> I taught an XML Interoperability course at the Washington DC ACM last
> week.  I had thirty-five students.  I asked how many had created XML
> vocabularies - about twenty-five.  (Only two are in production settings,
> though.)  I asked how many had used a namespace identifier on their
> vocabulary - one.
>
> People were genuinely aggravated by my suggestion that they define
> namespaces even in documents which use only one vocabulary.
>
> Seeing no namespace applied tends to remind me of that approach, and I
> figure it just combined with a namespace-using approach.

I think that namespaces are crucial to XML. The make XML extensible rather
than arbitrary. I always use namespaces sometimes I qualify everything,
sometimes I don't. It depends on what I'm doing.

>
> > And I think the shortcut has already been taken. If anything, this makes
it
> > safer by not fooling people into thinking they know how to process an
> > element based entirely on its local name and namespace name.
>
> So far as I've seen, you're the only person taking this particular
> shortcut.  I'd be interested to hear if there's anyone else who
> (independently) came to this approach.

Well, the SOAP world in general uses this style and I don't really see that
much difference between;

<xsl:transform xmlns:xsl='http://www.w3.org/2001/XMLSchema' >

  <xsl:param name='foo' />

  <xsl:template match='bar' >
    <xsl:param name='baz' />
  </xsl:template>

</xsl:transform>


<xsl:transform xmlns:xsl='http://www.w3.org/2001/XMLSchema' >

  <param name='foo' />

  <xsl:template match='bar' >
    <param name='baz' />
  </xsl:template>

</xsl:transform>

Both use local-scoping. Are you happier with the all-qualified approach with
local-scoping? Or do you think local-scoping is completely out?

Cheers

Gudge