Writing to XML file help

[alphawolf21]

<?php
$doc = new DOMDocument();
$doc->load("rss/updates.xml");
$doc->formatOutput = true;
include 'functions.php';
connect();
query("INSERT INTO updates(post,userid,subject,posted)VALUES('".addslashes($_POST["post"])."','".$_COOKIE["id"]."','".addslashes($_POST["subject"])."',CURRENT_TIMESTAMP)");
$n = mysql_insert_id();
loguser($_COOKIE["id"],"added an update to the site.");
$update = sql("SELECT subject,post FROM updates WHERE id = '".$n."'");
$rss = 	$doc->createElement("rss");
	$version = $doc->createAttribute("version");
	$version->value = "2.0";
	$nameSpace = $doc->createAttribute("xml:ns");
	$nameSpace->value = "http://www.w3.org/2005/Atom";
$rss->appendChild($version);
$rss->appendChild($nameSpace);
$channel = $doc->createElement("channel");
$item = $doc->createElement("item");
$title = $doc->createElement("title");
	$title->appendChild(
		$doc->createTextNode(stripslashes($update["subject"]))
		);
$link = $doc->createElement("link");
$link->appendChild(
	$doc->createTextNode("http://www.dreamspand.com/?act=updates")
);
 $post = $doc->createElement("description");
 	$post->appendChild(
   		$doc->createTextNode(substr(stripslashes($update["post"]),0,80)."..")
   	);
$item->appendChild($link);
$item->appendChild($title);
$item->appendChild($post);
$channel->appendChild($item);
$rss->appendChild($channel);
$doc->appendChild($rss);
$doc->saveXML();
$doc->save("rss/updates.xml");
echo "location.href='?act=updates';";
?>

This function writes and saves to an XML file, with one problem. It creates the RSS and channel elements each time I post an update into my database. How do I get it to just append the update elements to these tags without creating more? As in, how do I write within the rss/channel tags alone, and not just keep adding more of them to the file?

 

My XML file looks like this:

<?xml version="1.0"?>
<rss version="2.0" xml:ns="http://www.w3.org/2005/Atom">
  <channel>
    <item>
      <link>http://www.dreamspand.com/?act=updates</link>
      <title>t5</title>
      <description>f5..</description>
    </item>
  </channel>
</rss>
<rss version="2.0" xml:ns="http://www.w3.org/2005/Atom">
  <channel>
    <item>
      <link>http://www.dreamspand.com/?act=updates</link>
      <title>t6</title>
      <description>f6..</description>
    </item>
  </channel>
</rss>

I want it to look like this:

<?xml version="1.0"?>
<rss version="2.0" xml:ns="http://www.w3.org/2005/Atom">
  <channel>
    <item>
      <link>http://www.dreamspand.com/?act=updates</link>
      <title>t5</title>
      <description>f5..</description>
    </item>
    <item>
      <link>http://www.dreamspand.com/?act=updates</link>
      <title>t6</title>
      <description>f6..</description>
    </item>
  </channel>
</rss>

So if anyone has any ideas, I'd really appreciate it please. Otherwise this works fine, I'm just kinda lost.

[Skewled]

$rss = $doc->createElement("rss");
$version = $doc->createAttribute("version");
$version->value = "2.0";
$nameSpace = $doc->createAttribute("xml:ns");
$nameSpace->value = "http://www.w3.org/2005/Atom";

 

Above the values are assigned, then added to the XML file below:

 

$doc->appendChild($rss);