Issue 157 - XSLT and copy/replace semantics

["Ugo Corda" <UCorda@SeeBeyond.com>]

Rethinking about today's discussions on this subject, and also previous
discussions on the mailing list, I think there is a basic
misunderstanding of what the supporters of XSLT use in copy are saying
(at least some of the supporters - I don't think we have had enough
discussions for me to claim to represent all the XSLT proponents).

[Disclaimer: I am not proposing to get rid of copy and replace it with
XSLT - I am just claiming that *in some cases* XSLT can be used to
*achieve the same results* as the current copy]

Let me start from Yuzo's original example because it's very simple (I
modified it a little to make it even more clear and simple). Here is the
var1 variable with its contents:

var1: 

<invoice test="false">
        <invoiceNumber>9876</invoiceNumber>
        <orderNumber>0000</orderNumber>
        <amount/>
        <billingAddress><street/></billingAddress>
</invoice>

Now I want to modify this variable so that its contents looks like:

<invoice test="false">
        <invoiceNumber>9876</invoiceNumber>
        <orderNumber>1234</orderNumber>
        <amount/>
        <billingAddress><street>1
Somewhere</street><state>SW</state></billingAddress>
</invoice>

I could use the current copy and do something like:

<assign>
  <copy>
    <from><literal>1234</literal>,/from>
    <to>$var1/orderNumber</to>
  </copy>
  <copy>
    <from><literal><billingAddress><street>1
Somewhere</street><state>SW</state></billingAddress></literal></from>
    <to>$var1/billingAddress</to>
</assign>

(I am not completely sure the syntax I used above is aligned with the
latest 157 discussions, but you should get the idea of what I am talking
about).

Instead of doing that, I could use XSLT in the following way:

1) Here is the style sheet:

<xsl:stylesheet version="1.0"
    xmlns:xsl="http://www.w3.org/1999/XSL/Transform";>

    <xsl:template match="orderNumber">
        <xsl:element name="orderNumber">
            <xsl:value-of select="1234"/>
        </xsl:element>
    </xsl:template>

    <xsl:template match="billingAddress">
        <xsl:element name="billingAddress">
            <xsl:copy-of select= ... node corresponding to
"<billingAddress><street>1
Somewhere</street><state>SW</state></billingAddress>" ... />
        </xsl:element>
    </xsl:template>

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

    </xsl:template>

</xsl:stylesheet>

2) I take the tree contained in var1 - let's call it tree1

3) I apply the XSLT transform to tree1, yielding tree2

4) I replace the contents of var1 with tree2

5) the XSLT-based assign is done - if I look inside var1, its contents
are exactly the same as if I had used the two copy operations shown
before. In particular, I have achieved the same copy/replace semantics
of the current BPEL copy without in any way violating the semantics of
XSLT transformations (i.e. no modification of tree1)


Ugo