site path

Hello guys I'm just looking for some advise: I've got a variable which I use to store my site's main path. Is it better to have it like this: $site_path = "/my/web/path/" or like this: $site_path = "http://my_url.com/" ? What about the trailing slash?, should I use it or not? I know these are simple question but haven't been able to get to an answer on my own. Thanks a lot ******************************************************* Wilmar Pérez Network Administrator Library System Tel: ++57(4)2105145 University of Antioquia Medellín - Colombia 2002 *******************************************************