Re: [xml-dev] RE: Namespace use cases

[Kurt Cagle <kurt.cagle@gmail.com>]

Micah,

On #3, I'd clarify this point a bit:

* It must be possible for a document processor, upon encountering an
element in an unknown namespace, to locate a downloadable processor on
the web, in order to complete processing of the document.

I'd call this the Naive Interpretation of namespaces, and it is unfortunately pervasive. There is, of course, an identification aspect to a namespace - in theory, if I have a namespace for class foo (svg is a good example), then the browser should be able to search through a LUT in order to retrieve the internal processor for this namespace, or it should be able to degrade nicely (i.e., the contents should in fact not be displayed at all). I think that this is in fact an extremely important use case for namespaces in the HTML case. But the idea that the browser should be able to extend functionality based upon an external, downloadable processor, while certainly a "cool idea" from the technical standpoint, would seem to me to be a security nightmare. 

It does make me wonder, though, if at least some part of the problem that the HTML side has with namespaces is precisely because of the Naive Interpretation. 

Kurt Cagle
Managing Editor
http://xmlToday.org

On Mon, Jul 13, 2009 at 6:26 PM, Micah Dubinko <micah.dubinko@marklogic.com> wrote:

This is a useful way to think about the use cases. Particularly in the context of HTML:

#1 is critical. This falls under what the W3C calls "decentralized extensibility", and is floating to the top of their awareness as a problem.

#2 seems like it is probably important in some guise, but I'd like to see more specific cases.

#3 may be a non-issue *for HTML*. One reason why this case gets less attention is that is no consensus exists that using namespaces as a major version number is a best practice (see, for example, the one namespace vs three debates from another era of XHTML)

Like I mentioned, I'm interested in the HTML use cases based on recent developments. One particular aspect is negative cases. For instance, I'm pretty sure there are still people out there who think this was/(is??) a requirement of xmlns:

* It must be possible for a document processor, upon encountering an element in an unknown namespace, to locate a downloadable processor on the web, in order to complete processing of the document.

Which is an unfortunate burden to bear. Thinking like this has led to countless billions of uses of the string "http://www" in ugly unmemorable namespace strings with very little resulting benefit, and in fact a great deal of confusion. It's too late to fix this in XML, but not too late for HTML.

So let's dig in to some usage details. Are there other parts of xmlns that are over-engineered for use in HTML?

I'd like to see more examples too. What are some examples of namespaces widely used in HTML? Are any of them from outside the W3C?

Thanks, -m

On Jul 11, 2009, at 3:06 AM, rjelliffe@allette.com.au wrote:

I think there are three distinct cases.

#1

The first is the declarations used for namespaces on elements and
attribute names: the subject of the Namespaces in XML spec. This took
multiple thousands of emails last time, so good luck on it this time.

#2

The second is the namespaces used for Qnames in element and attribute
values. XSLT went one way, but I think it is the wrong way because it
fudges the difference between data and markup. Schematron has explicit
elements and this has been very smooth: developers don't worry about
default namespaces, they only need to look in a single place.

#3

The third is that the role of namespace is challenged by emerging
maintenance requirements. The generation of schemas developed without
version attributes now face the challenge of how to cope when they need a
major version upgrade, and namespaces are the obvious and (I think)
correct thing to use as a slicker kind of major version number. (It is not
that I am trying to say that namespace = schema, however namespace = major
version = schema family or base schema is OK.)

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