Loop through an XML with parameters and outputting them as a list?

I have an XML file and the data is passed through parameters, like so:

<node id="a" title="Title A">
    <node id="b"  title="Title B">
       <node id="c"  title="Title C">
       </node>
    &开发者_运维技巧lt;/node>
    <node id="d"  title="Title D">
    </node>
</node>

How can I loop recursively through this XML and print only the ID of every node in a list? i.e.

<ul>
   <li>a</li>
   <ul>
      <li>b</li>
      <ul>
         <li>c</li>
      </ul>
   </ul>
   <ul>
      <li>d</li>
   </ul>
</ul>

Although it would be possible without xslt, I think this is more reusable:

<?php
$dom = new DOMDocument();
$dom->loadXml('<node id="a" title="Title A">
    <node id="b"  title="Title B">
       <node id="c"  title="Title C">
       </node>
    </node>
    <node id="d"  title="Title D">
    </node>
</node>');


$xsl = new DOMDocument;
$xsl->loadXml('<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
    <xsl:template match="/">
        <ul><xsl:apply-templates /></ul>
    </xsl:template>

    <xsl:template match="node">
        <li><xsl:value-of select="@title" /> (<xsl:value-of select="@id" />)
            <xsl:if test="count(descendant::node) > 0">
                <ul><xsl:apply-templates /></ul>
            </xsl:if>
        </li>
    </xsl:template>
</xsl:stylesheet>', LIBXML_NOCDATA);

$xslt = new XSLTProcessor();
$xslt->importStylesheet($xsl);

echo $xslt->transformToXML($dom);

If you need to have access to the nodes before printing you can do it by using simplexml_load_string:

<?php

$str = '<node id="a" title="Title A">
    <node id="b"  title="Title B">
       <node id="c"  title="Title C">
       </node>
    </node>
    <node id="d"  title="Title D">
    </node>
</node>';

$xml = simplexml_load_string($str);

print_r($xml);
?>

To access the child nodes

$xml = simplexml_load_file('test.xml');
var_dump($xml);

foreach($xml as $node){
    foreach($node->attributes() as $key=>$val){

        echo $key.'-'.$val.'-';
    }
}