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Re: Chameleon Component Summary & Proposal

From: Innovimax SARL <innovimax@gmail.com>
Date: Sat, 17 Feb 2007 18:12:27 +0100
Message-ID: <546c6c1c0702170912o27bc196er62c90cf9cfd5afc4@mail.gmail.com>
To: "Alex Milowski" <alex@milowski.org>
Cc: public-xml-processing-model-wg@w3.org

On 2/16/07, Alex Milowski <alex@milowski.org> wrote:
> This is my summary... so correct me if I'm wrong.
>
> We started this discussion because we needed to distinguish between
> component configuration parameters and parameters to the component
> itself.

Thank you for restating this

> In the former case (configuration parameters), these parameters are
> often use to select the right underlying implementation technology
> (e.g. XML Schema vs Relax or XSLT 1.0 vs 2.0).  The latter case, the
> parameters are application parameters to particular component
> technologies ( e.g. parameters to a stylesheet).
>
> The issue of configuration parameters brought up the label "chameleon"
> because the underlying implementation might be choosing between
> "actual" components ( e.g. a Relax validation engine versus an XML Schema
> processor).
>
> In addition, these parameters are quite distinct in that configuration
> parameters are allowed to cause the pipeline to fail to compile.  For
>  example, a configuration parameter of "version" with a value of "2.0"
> to an XSLT component would require that the implementation support XSLT
> 2.0.  If it can't support XSLT 2.0, it can't run the transform and should
> fail to compile the pipeline.
>
> While application parameters might cause a pipeline to fail to run, they
> are often dynamic errors as a result of running the component.  Handling
> of such application error should be able to be caught and dealt with
> by our try/catch construct.
>
> In addition, we need a way to preserve our current open content models
> for the pipeline language so that authors can add arbitrary documentation or
> annotations and not have them be thought as component types.
>
> On the call, several people voiced the idea that we want to be able to
> specify namespaces as "ignorable" so that we can have annotations or
> document elements and keep an open content model.  Basically, if an
> element is not ignored it had better be one of the ones we define in our
> specification or we must have a component definition associated with it.
>
> Here's my proposal based on what I've heard so far:
>
>    * An element in the pipeline document must be:
>        * in our namespace where our specification defines the semantics
>        * identified as a step element via a component definition
>        * identified as ignoreable via the element's namespace.
>
>    * Add an optional attribute on the [p:]pipeline element of
> 'ignore-prefixes'
>      that has a list of namespace prefixes.   Each of those prefix
>      identify elements that should be ignored while loading the pipeline
> document.
>
>    * By default, elements in the "no namespace" is ignored.
>
>    * Ignored elements have no semantics and the pipeline processor should
>      act the same as when given a document where those ignored elements
>      are deleted.
>
>   * Any component type can be written as a step as an element whose name
>     is the component type (e.g. <p:xslt ...></p:xslt>)  This element has a
> required
>     attribute of 'name'  and whose content model is the same as the now
> "abstract"
>     element [p:]step.  I'll call this element the "component step element".
>
>   * A configuration parameter is specified on the component step
>     element by a simple typed attribute.  The value of that configuration
>     parameter is a string value.
>
>     Note: In the future, we could pass the simple type value.
>
>     Note: We can't have a configuration parameter named 'name' that has a
> different
>      value than the name of the step.  Although, having the name accessible
> as
>     a configuration parameter will be very nice for debugging.
>
>   * All application parameters are specified via the [p:]parameter element
> as
>     we specify in our current document (the status quo).
>
> I believe that is the core of what we have talked about.
>
> Considering appropriate defaulting of ports, this gives us steps like:
>
> <p:xslt version="2.0">
>    <p:input port="transform">
>        <p:document href="stylesheet.xsl"/>
>    </p:input>
> </p:xslt>
>
> where we're forcing an XSLT 2.0 implementation.
>
> <p:xslt version="2.0" mode="toc">
>     <p:input port="transform">
>         <p:document href="stylesheet.xsl"/>
>     </p:input>
>  </p:xslt>
>
> where we're asking for initial mode 'toc' and so on.
>
> For validation, we get:
>
> <p:validation
> language="http://www.w3.org/2001/XMLSchema/v1.1 ">
>     <p:input port="schema"> ... </p:input>
> </p:validation>
>
> Things we might consider:
>
>   * allow definitions of configuration parameters in the component
> definition.  This
>     would be necessary to generate an appropriate schema type/element
> declaration
>     for the component step element.
>
>   * allow configuration parameters to be child elements of the component
> step
>     elements.
>
> That last point I find really interesting.  I think it would simplify
> setting configuration
> parameters that have large text values as well as allow for lists.
>
> Here's my examples:
>
> 1. The "munge" component that fetches a resource and makes it
>      available after converting it to base64 for application data or running
> tidy on
>      HTML.  Here I want to specify a set of mime types that it should
> accept:
>
>     <my:munge name="get.resource">
>        <my:mime-type>application/pdf</my:mime-type>
>        <my:mime-type>image/jpeg</my:mime-type>
>        <my:mime-type>text/html</my:mime-type>
>     </my:munge>
>
>    Here the component receives configuration parameter 'my:mime-type' that
> has a
>    value of a list of mime type values.
>
>  2. A simple ruby script component that needs the script to run.
>
>    Currently, I could write:
>
>    <p:step type="j:ruby" name="reverse.ABC">
>       <p:param name="j:script" value="puts &quot;&lt;doc>&quot; +
> &quot;ABC&quot;.reverse + &quot;&lt;/doc>&quot;"/>
>     </p:step>
>
>    this proposal makes this:
>
>    <j:ruby name="reverse.ABC">
>        <p:param name="j:script" value="puts &quot;&lt;doc>&quot; +
> &quot;ABC&quot;.reverse + &quot;&lt;/doc>&quot;"/>
>      </j:ruby>
>
>    but I'd rather write:
>
>    <j:ruby name="reverse.ABC">
>       <j:script>
>       <![CDATA[
>          puts "<doc>" + "ABC".reverse + "</doc>"
>       ]]>
>       </j:script>
>     </j:ruby>
>
>
>    In all cases the component receives a configuration parameter of
> 'j:script" containing
>    the ruby code to execute.
>
> 3. Specifying xquery pragmas and options
>
>    <p:xquery>
>       <pragma>(# exist:batch-transaction #)</pragma>
>       <pragma>(# exist:timer #)</pragma>
>       <option>exist:serialize "method=xhtmll"</option>
>    </p:xquery>
>
> --
> --Alex Milowski
> "The excellence of grammar as a guide is proportional to the paucity of the
> inflexions, i.e. to the degree of analysis effected by the language
> considered."
>
> Bertrand Russell in a footnote of Principles of Mathematics

Here are the most important objections
* Configuration parameters could no more be complexType (unless the
option of allowing configuration parameter to be children is retained)
* How can we define a configuration parameter at runtime ?
* It sounds like the language to define user component will look like
rocket science
* ignore-prefixes : what will happen if a prefix appear in a here document ?

In your examples
* There is no mention for user defined components of input and output,
where do they live ?

Ahead of that
* p:xslt is too specific compared to p:validate (should be p:transform
or p:xml-schema)

Regards,
Mohamed

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Received on Saturday, 17 February 2007 17:12:34 GMT

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