Here's a function to canonicalize a URL containing relative paths. Ran into the problem when pulling links from a remote page.

<?php

function canonicalize($address)
{
    $address = explode('/', $address);
    $keys = array_keys($address, '..');

    foreach($keys AS $keypos => $key)
    {
        array_splice($address, $key - ($keypos * 2 + 1), 2);
    }

    $address = implode('/', $address);
    $address = str_replace('./', '', $address);
}

$url = 'http://www.example.com/something/../else';
echo canonicalize($url); //http://www.example.com/else

?>