Architectures which are built on top of a blackboard system. A blackboard system can be considered an architeure itself, which organizes communication between modules and gives explicit structure to the knowledge. Blackboards also include a control system which determines the oder of processing of the information on the blackboard. Therefore, architectures built on top of such systems are constraind by the same properties. The prototypical system built on a blackboard is the Guardian system, by (B. Hayes-Roth)