Acquiring Primary and Secondary Assumptions in BGP-MS

User modeling components should include suitable mechanisms for acquiring user models, in addition to representation and management mechanisms. The methods developed to date can be divided into two groups: Those that extract primary assumptions about the user from his/her system input; and those that extract secondary (or derivative) assumptions from primary and other secondary assumptions. Secondary assumptions may be derived as soon as this is possible (e.g., immediate forward chaining as soon as new primary assumptions have been made), or their derivation may be deferred until they are needed (e.g., backward chaining triggered by a query to the user model).