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Re: Namespace bindings

From: Jeni Tennison <jeni@jenitennison.com>
Date: Tue, 07 Aug 2007 10:17:40 +0100
Message-ID: <46B838B4.1030107@jenitennison.com>
To: public-xml-processing-model-wg@w3.org

Norman Walsh wrote:
> Do we expect the following pipeline to work?
> 
> <p:pipeline xmlns:p="...">
>   <p:option name="delete" value="html:div"
>             xmlns:html="http://www.w3.org/1999/xhtml"/>
> 
>   <p:delete>
>     <p:input port="source">
>       <p:inline>
>         <html xmlns="http://www.w3.org/1999/xhtml">
>         <head>...</head>
>         <body>
>           <h1>Delete My Divs</h1>
>           <div>
>             ...
>           </div>
>         </body>
>       </p:inline>
>     </p:input>
> 
>     <p:option name="match" select="$delete"/>
>   </p:delete>
> </p:pipeline>
> 
> Where "work" means that the pipeline runs and produces:
> 
> <html xmlns="http://www.w3.org/1999/xhtml">
> <head>...</head>
> <body>
>   <h1>Delete My Divs</h1>
> </body>

Yes, I think we have to support this.

> Suppose local.xml contains:
> 
>   <commands>
>     <delete xmlns:h="http://www.w3.org/1999/xhtml"
>             match="h:div"/>
>   </commands>
> 
> Do we expect this to work?
> 
> <p:pipeline xmlns:p="...">
>   <p:load name="load-commands" href="local.xml"/>
> 
>   <p:delete>
>     <p:input port="source">
>       <p:inline>
>         <html xmlns="http://www.w3.org/1999/xhtml">
>         <head>...</head>
>         <body>
>           <h1>Delete My Divs</h1>
>           <div>
>             ...
>           </div>
>         </body>
>       </p:inline>
>     </p:input>
> 
>     <p:option name="match" select="/commands/delete/@match">
>       <p:pipe step="load-commands" port="result"/>
>     </p:option>
>   </p:delete>
> </p:pipeline>

Yes, I think we should support this too.

Here's a proposed wording:

Each option value has a set of namespace bindings associated with it. 
The namespace bindings used depend on the way in which the option is 
specified, as follows:

(a) if the option is specified with the value attribute, the namespace 
bindings are the set of namespace bindings on the <p:option> element itself.

(b) otherwise, if the select attribute contains a single variable 
reference, the namespace bindings are set of namespace bindings from the 
referenced option.

(c) otherwise, if the result of evaluating the select attribute is a 
node, the namespace bindings are the in-scope namespaces from that node.

(d) otherwise, the namespace bindings are the union of:
     i)  the namespace bindings on the <p:option> element
     ii) the namespace bindings of all options referenced in the select
         attribute
     It is a dynamic error (ERR:XXXXX) if there's more than one 
namespace binding for a given prefix with different namespace URIs.

---

A variation on the above would be to exclude the default namespace from 
the set of namespace bindings that are associated with the option. If 
the default namespace *isn't* excluded (as above), you'll get more 
errors under (d) than you would if it *were* excluded. But if they *are* 
excluded, then QNames won't work in the normal-for-XSD way. I'm inclined 
to stick with it as it is above: if you get to (d) then you're going to 
have to take great care with namespaces anyway.

(I don't know if QNames in XProc usually work in the normal-for-XSD way, 
using the default namespace for unprefixed names, or the 
normal-for-XPath way, using no namespace for unprefixed names? For 
example, what if the value of the type attribute on <p:pipeline> doesn't 
have a prefix? I don't recall seeing any statement about this, but maybe 
I missed it.)

Also, suppose local.xml contains:

   <commands>
     <delete xmlns:h="http://www.w3.org/1999/xhtml"
             match="h:div"/>
   </commands>

In this case, the following pipeline *won't* work:

<p:pipeline xmlns:p="..." xmlns:html="http://www.w3.org/1999/xhtml">
   <p:load name="load-commands" href="local.xml"/>

   <p:delete>
     <p:input port="source">
       <p:inline>
         <html xmlns="http://www.w3.org/1999/xhtml">
         <head>...</head>
         <body>
           <h1>Delete My Divs</h1>
           <div>
             ...
           </div>
         </body>
       </p:inline>
     </p:input>

     <p:option name="match"
        select="concat('html:body/', /commands/delete/@match)">
       <p:pipe step="load-commands" port="result"/>
     </p:option>
   </p:delete>
</p:pipeline>

because the only namespaces passed into the match option are the ones on 
the <p:option> (it falls under (d) above).

But you can make it work by defining an intermediate option like this:

<p:pipeline xmlns:p="..." xmlns:html="http://www.w3.org/1999/xhtml">
   <p:load name="load-commands" href="local.xml"/>

   <p:group>
     <p:option name="local-match" select="/commands/delete/@match">
       <p:pipe step="load-commands" port="result"/>
     </p:option>

     <p:delete>
       <p:input port="source">
         <p:inline>
           <html xmlns="http://www.w3.org/1999/xhtml">
             <head>...</head>
             <body>
               <h1>Delete My Divs</h1>
               <div>
                 ...
               </div>
             </body>
           </html>
         </p:inline>
       </p:input>

       <p:option name="match"
         select="concat('html:body/', $local-match)" />
     </p:delete>
   </p:group>
</p:pipeline>

because in this case the $local-match will have the namespace bindings 
from local.xml, and the match passed into the <p:delete> will union 
these with the ones on the <p:option>.

Cheers,

Jeni
-- 
Jeni Tennison
http://www.jenitennison.com
Received on Tuesday, 7 August 2007 09:17:45 GMT

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