Well this is just a little, everyday task: I’m currently working on the Sto International Website and needed to modify an XML file so that each of its nodes has a unique ID assigned. The fastest way to achieve this is a very simple XSL transformation like the one below:

<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
    version="1.0">
    <xsl:output method="xml" indent="yes" />
    <!--
        This stylesheet just assigns a unique ID
        to each node in the XML tree
    -->
    <xsl:template match="/">
        <xsl:apply-templates />
    </xsl:template>
    <xsl:template match="*">
        <xsl:element name=" { name ( ) } ">
            <xsl:attribute name="nodeID">
                <xsl:value-of select="generate-id ( ) " />
            </xsl:attribute>
            <!-- copy any other attributes -->
            <xsl:for-each select="attribute::*">
                <xsl:copy />
            </xsl:for-each>
                <!-- and do everything recursively -->
            <xsl:apply-templates />
        </xsl:element>
    </xsl:template>
</xsl:stylesheet>

You can use fairly any XSLT processor you want to let it do the job. In my case (Mac OS X), I just did it on the command line with xsltproc (Syntax: -o output-file.xml stylesheet.xsl input-file.xml):

Xor:sto02 gertz$ xsltproc -o out.xml idmaker.xsl input.xml