[xslt] xforms processor in pure xslt

[Bernhard Zwischenbrugger <bz datenkueche com>]

I try to implement a (server side) xforms (http://www.w3.orf/xforms) processor
in pure xslt.

It's not very difficult to do that, but there is one thing I can't solve.
Maybe the concept is wrong, but maybe there is a simple solution.

The xforms processor should translate xhtml+xforms to html+forms.
There will be a second XSLT Stylesheet that evaluates the URL (including GET 
data) and generate a new XML File (data.xml).

Please have a look at the following example:

XHTML+XForms (model.xml)
============

<?xml version="1.0" encoding="ISO-8859-1" ?>
<!-- -->
<!-- this is a simplified xforms example -->
<!-- this is pseudo code only -->
<!-- -->
 
<form xmlns:xfm="http://www.w3.org/2000/12/xforms"   
          xmlns="http://www.w3.org/2000/xhtml">
 
        <xfm:xform id="form1">
                <xfm:instance id="instance1" xlink:href="data.xml" />
        </xfm:xform>
 
 
        <h1>XForms model in X-Smiles</h1>
        <p>The model in XForms defines the allowed content of form fields</p>
        <xfm:textbox xform="form1" ref="/all/one" cols="20">
                <xfm:caption>Name</xfm:caption>
                <xfm:instance>/all/one</xfm:instance>
        </xfm:textbox>
 
</form>

XSLT:
=====

<?xml version="1.0" encoding="UTF-8"?>
<!--  -->
<!-- (C) 2001 LGPL-->
<!--     author:Bernhard Zwischenbrugger -->
<!--     email: bz@datenkueche.com
<!-- -->
<!-- This isn't a working example !! -->
<!--  -->
<xsl:stylesheet
        version="1.0"
        xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
        xmlns:libxslt="http://xmlsoft.org/XSLT/namespace"
        xmlns:xfm="http://www.w3.org/2000/12/xforms"
        xmlns:xlink="http://www.w3.org/2000/xlink"
        xmlns="http://www.w3.org/2000/xhtml"
        >
<xsl:output method="html" version="1.0" encoding="UTF-8" indent="yes"/>
 
<!-- -->
<!-- copy html to output, replace xforms by html forms -->
<!-- -->
<xsl:template match="*">
        <xsl:choose>
        <xsl:when test="self::xfm:*">
                <xsl:call-template name="xforms"/>
        </xsl:when>
        <xsl:otherwise>
                <xsl:element name="{name()}">
                <xsl:for-each select="@*">
                        <xsl:attribute name="{name()}" select="{text()}"/>
                </xsl:for-each>
                <xsl:apply-templates select="*|text()"/>
                <xsl:value-of select="text()"/>
                </xsl:element>
        </xsl:otherwise>
        </xsl:choose>
</xsl:template>
 
<!-- -->
<!-- select the xforms -->
<!-- -->
<xsl:template name="xforms">
        <xsl:value-of select="xfm:caption"/>
        <!-- Textbox -->
        <xsl:if test="name()='xfm:textbox'">
                <xsl:call-template name="textbox"/>
        </xsl:if>
        <br/>
</xsl:template>
 
<!-- -->
<!-- translate xforms elements to html forms -->
<!-- -->
<xsl:template name="textbox">
        <input type="text" action="{@xform}" name="{@ref}" size="{@cols}">
                <xsl:attribute name="value">
                        <!-- -->
                        <!-- #### Here is the big problem ####-->
                        <!-- -->
                        <xsl:value-of 
select="libxslt:node-set(document(//xfm:form/xfm:instance/@href)/$instance)"/>
                        <!-- -->
                        <!-- #### End of big problem ####-->
                        <!-- -->
                </xsl:attribute>
        </input>
</xsl:template>
 
</xsl:stylesheet>

data.xml
======
<?xml version="1.0"?>
<all>
        <one>first</one>
        <two>second</two>
</all>

The problem is to get values from data.xml to fill the
form elements with default data.
It's possible to get the path to the data.xml from model.xml.
But as I know, it isn't possible to get an xpath value from model.xml
and select a value from data.xml using the xpath of the <instance> tag
in the model.xml.

Is there a simple solution for this problem?
Is it possible to write an extension function for this?

I know, using DOM it shouldn't be a big deal to imlement an xforms
processor, but XSLT is the language I like.

thanx

Bernhard