BASE.XML
BASE.XML defines base types for lists that apply globally to all the team Web sites on a server running SharePoint Team Services from Microsoft. It is located at Program Files\Common Files\Microsoft Shared\web server extensions\50\Templates\1033\xml.
This file provides the schemas used in creating the List of Lists, Views, Projects, URLs (DocMd), and People (UserInfo) tables in the database when a new site is provisioned.
Users should not try to modify this file.