The current startup sequence when a webpage is selected works something like this

1. The URL is most likely re-written by the mod_rewrite directives in .htaccess. For new sites the URL will always resolve to index.php
2. Index.php looks in it's document root for Application.php. This looks for the file SiteConfig.php along the path the request was made from. (Eventually we will do away with Application.php and move that code into index.php once we have removed the shared-www folder)
3. SiteConfig.php has details about the specific website and lives in sites/sitedir. It includes GlobalConfig.php that lives in the sites directory.