Re: [xml-dev] Pragmatic namespaces

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From: "Pete Cordell" <petexmldev@codalogic.com>
To: "Micah Dubinko" <micah.dubinko@marklogic.com>,"XML Developers List" <xml-dev@lists.xml.org>
Date: Mon, 3 Aug 2009 19:56:58 +0100
I'm not convinced about the merits of reversing the domain name part of a 
name other than Java does it.

Java has an additional requirement that an import statement must be able to 
track down a relevant file, and mapping the import name to a file hierarchy 
helps with this.  XML/HTML tag naming doesn't have this requirement.

So I suggest using non-reversed domain names.  For instance, I think your 
example would be better written as:

<head>
   <title>Document title</title>
   <project.example.com>
     <id.example.com>123521123</id.example.com>
   </project.example.com>
</head>

I think this has a number of benefits:

- You don't have to explain to non-programmers how to reverse a domain name!

- Although a minor concern, all other things being equal it should be more 
efficient to parse as the entropy is at the start of the string making it 
easier to look up.

- IDE code completion tools should work a lot better making editing 
documents much easier.

- But most importantly, IMO the eye gravitates to the '<' character when 
looking for an element name.  Separating the local name from the '<' 
character, potentially by some distance, makes the document harder to read. 
And in the majority of cases the first part of the name is likely to 
non-conflicting, and a lot of the time you would never have to look at the 
domain part.

Thanks,

Pete Cordell
Codalogic Ltd
Interface XML to C++ the easy way using XML C++
data binding to convert XSD schemas to C++ classes.
Visit http://codalogic.com/lmx/ or http://www.xml2cpp.com
for more info

----- Original Message From: "Micah Dubinko"



Literally for years, people have been talking about how great it would
be to use something like Java-style namespaces in XML instead of the
current xmlns regime. For example 
<http://www.xml.com/pub/a/2005/04/13/namespace-uris.html
 > .

By scoping the solution down to just HTML syntax, I believe a
reasonable solution can be crafted, and now that the W3C is focusing
on "distributed extensibility" as a requirement for HTML5, the timing
seems right to see how far a proposal in this direction can go. On the
other hand, if this proposal doesn't work out, maybe it will
permanently end the musings about how great Java-style namespaces
would be.

I'm posting this on xml-dev for community input and feedback. I have
no current association with the HTML Working Group, and this is my
personal project, with no reflection on my employer. The format is an
intermingling of requirements and proposed solutions. This is largely
inspired by Tom Bradford's "clean namespaces" proposal, the
archive.org version of which I linked to previously.

Requirement: Ask not if it is good enough, ask if it can be popular
enough.

(Thanks to Douglas Crockford for the quote). This proposal will
horrify the purists, but that's OK.

Requirement: this solution must not interfere with existing HTML
elements or attributes

Point 1:
Any element name with no dots in it is treated as HTML (including HTML
rules on handing unrecognized elements)

Requirement: this solution must allow for distributed creation of
globally-unique namespace names (including those outside of a
consensus process)

Point 2:
Any element with one or more dots in it is treated as an extension
element. The portion after the last dot is considered the localname,
and the the portion up to but not including the last dot is parsed as
the pragmatic namespace name (or pname for short). Interfaces with
existing namespace-aware APIs must treat the pname as the namespace
URI. With the exception noted below, to prevent clashes pnames must be
based on reversed DNS names.

Example:
<head>
   <title>Document title</title>
   <com.example.project>
     <com.example.id>123521123</com.example.id>
   </com.example.project>
</head>

In this example document.getElementsByTagName("id") would return the
innermost element.
So would document.getElementsByTagNameNS("com.example", "id")

Requirement: it is highly desirable to produce a document that will
produce the same element names in HTML or XML

Point 3:
Zero or more special attributes of the form using.<pname> may appear
on the root element, and ONLY on the root element. The declarations
have document-wide scope. The pname that appears after "using." is the
one being declared. The value of the attribute is a space-separated
list of localnames that represent boundary elements, in other words,
upon reaching a boundary element, a new namespace gets applied to that
element and all children (until encountering another boundary element).

Example equivalent to the previous:
<html using.com.example="project">
<head>
   <project>
     <id>123521123</id>
   </project>
</head>

This structure will produce the same element names in an XML parser,
and a straightforward transformation could convert it to true XML
+Namespaces.

Requirement: widely-known namespaces must be parse to an equivalent
DOM as xmlns

Point 4:
In any extension element with only one dot, the token before the first
dot is treated specially. Specifically, there exists a list of
grandfathered namespaces, and associated namespace URIs. Interfaces
with existing namespace-aware APIs must treat the grandfathered
namespace URI as the namespace URI of the extension element.

Here is the list: (additional suggestions welcome)

atom http://www.w3.org/2005/Atom
docbook http://docbook.org/ns/docbook
html http://www.w3.org/1999/xhtml
math http://www.w3.org/1998/Math/MathML/
svg http://www.w3.org/2000/svg
xbl http://www.mozilla.org/xbl
xbl2 http://www.w3.org/ns/xbl
xforms http://www.w3.org/2002/xforms
xlink http://www.w3.org/1999/xlink
xml http://www.w3.org/XML/1998/namespace

Example:

<html using.math="math">...
<p>
E.g. <math><msqrt><mi>π</mi></msqrt></math>
</p>
...</html>

In this example document.getElementsByTagName("mi") would return the
innermost element.
So would 
document.getElementsByTagNameNS("http://www.w3.org/1998/Math/MathML/
", "mi")

Requirement: must support HTML nested inside an extension vocabulary.

Point 5:
Unless overridden, HTML documents are treated as if all localnames
explicitly listed in the specification are HTML boundary elements.

Example:
<html using.svg="svg">
   <body>
     <svg version="1.1"  viewBox="0 0 100 100"
preserveAspectRatio="xMidYMid slice">
       <rect x="10" y="10" width="100" height="150" fill="gray"/>
       <foreignObject x="10" y="10" width="100" height="150">
         <body>
           <div>Here is a <strong>paragraph</strong>.</div>
         </body>
       </foreignObject>
     </svg>
   </body>
</html>

Here the inner body element and its children are still treated as HTML.

Another example:
<html using.xforms="model select1 range secret">
   <head>
     <model>...</model>
   </head>
   </body>
     <xforms.input>...
   </body>
</html>

In this case, "input" is already used as an HTML element name, so uses
of it--even with the using statement at the top--need to be explicitly
spelled out. Of course, the author could have overridden this by
including "input" in the using statement, but then any regular HTML
input controls would need to be spelled <html.input>. Just like in Java.

That's the entire proposal.

In practice, it may be inevitable that browser makers might bake in
additional defaults, like
using.math="math mi mo ms mn mtext"
such that users can freely use chosen vocabularies with zero
additional markup. Support for this outcome is an additional feature
of this proposal.

---

I will be at Balisage this year. If you have comments or ideas, look
me up. Comments on this list are welcome as well.



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Follow-Ups:
- Re: [xml-dev] Pragmatic namespaces
  - From: Micah Dubinko <Micah.Dubinko@marklogic.com>
- RE: [xml-dev] Pragmatic namespaces
  - From: "Michael Kay" <mike@saxonica.com>
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