Still, I don't see any need for path.
Let's have t this way.
1. A participant logs in. He has an unique identifier, say, $user_id.
2. He sends a file. Then you store it as $user_id.$filename or you create a folder $user_id and store the file in this folder with any name you like, or whatever.
Then the only thing you have to do is to make the file accessible to its owner only. For example, you can make all these files unaccessible via http and serve them through a script showfile.php like this:
$user_id = $_SESSION['user_id'];
// Let's assume you use sessions//
$filename = get_file($user_id);
// you can store filename in db or
// search user's folder for any files...
// anyway, you get it depending on what $user_id is.
$file = file($filename);
foreach ($file as $string)
echo $string;
Hope This Helps.
