transforming a XML on the basis of another XML

Diex75 · November 9th, 2006, 07:23 AM

Hi everybody,

I'm looking for a special kind of XSLT.

This is the situation:

I'm receiving a 'default XML' from some component with an unknown format. I don't know what tags it has or how many.

Then another XML comes to me from another component. This second XML tells me how to transform the first. Let's call this second XML the 'changes XML'.
It might tell me something like this:

<DELETE xpath="/books/authors/murakami" />
<EDIT xpath="/configuration/compiler@language" newValue="python" />
<ADD xpath="//customers" nodeType="element" name="age" value="9 years" />

I still don't know what the 'default XML' looks like, except that it probably contains the nodes mentioned in the 'changes XML'.

The question is: is there a neat solution thinkable, using XSLT?

Personally I was thinking that the 'changes XML' could be made into a XSLT which then transforms the 'default XML'.

Any ideas are welcome?

mhkay · November 9th, 2006, 08:31 AM

Yes, this is actually quite a common design pattern. Think of your "changes XML" as being the specification of a transformation in some peculiar language. Then write a translator that converts this language to XSLT. The translator, of course, can be written in XSLT.

Michael Kay
http://www.saxonica.com/
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference

Diex75 · November 9th, 2006, 08:45 AM

I'm wondering. What if my 'changes XML' would be empty, how would the XSLT for the 'default XML' look like?
Effectively this would be a XSLT that leaves the 'default XML' unchanged.
Since I'm new to XSLT, could someone show me what this 'minimalistic' XSLT should look like?

joefawcett · November 9th, 2006, 08:49 AM

Have a look at the identity XSLT on Google or this forum's old posts, it's basically:

Code:

<xsl:stylesheet version="1.0"
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:template match="@*|node()">
    <xsl:copy>
      <xsl:apply-templates select="@*|node()"/>
    </xsl:copy>
  </xsl:template>
</xsl:stylesheet>

You can add extra templates that apply to specific nodes to perform specialised tasks. E.g to delete all SOMETHING elements and their content add:

Code:

<xsl:template match="SOMETHING"/>

--

Joe (Microsoft MVP - XML)

mhkay · November 9th, 2006, 09:11 AM

To write an identity transform, the best way is to have a stylesheet containing the single template rule:

<xsl:template match="node()|@*">
  <xsl:copy>
    <xsl:apply-templates select="node()|@*"/>
  </xsl:copy>
</xsl:template>

This walks the tree copying every node as it goes. You can then add extra template rules to define customized behaviour for nodes that you want to modify.

Michael Kay
http://www.saxonica.com/
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference