Master Rule Collection 
SAP NetWeaver Portal supplies a default rule collection object named Master Rule Collection (main_rules). The portal runtime analyzes the display rules defined in this object to determine which portal desktop to provide to users when they log on to the portal.
Location in Portal Catalog: Portal Content > Portal Administrators > Super Administrators > Master Rule Collection (main_rules) (pcd:portal_content/administrator/super_admin/main_rules).
Caution
Do not delete or move this rule collection object. Without this object, the portal runtime cannot assign a desktop to users logging on to the portal.
Integration
If you are using additional rule collection objects in the Portal Catalog, you must add them to the Master Rule Collection object as nested conditions for them to take effect.
Features
By default, the Master Rule Collection object contains the following condition:
IF User = *
THEN Portal Desktop = pcd:portal_content/every_user/general/defaultDesktop
This is a generalized condition (where the parameter type User is defined as a wildcard value) that assigns the default portal desktop supplied with the portal (see Default Portal Desktop) to any user logging on to the portal.
Typically, this condition should be maintained as the last condition in the Master Rule Collection object, thus providing a fallback option if the rule collection does not specify a desktop assignment for every possible user or scenario. Nevertheless, if the portal is unable to resolve a portal desktop for a given user based on the defined display rules, even without the aforementioned condition, the Default Portal Desktop desktop object is automatically given to the user.