The system activity model is a static, hierarchic, normative representation of control that includes operator commands as well as commands and actions that comprise automated procedures. Higher levels of the model include tasks and functions which the lower level control actions support. The lowest level of the model describes direct interactions with the system, such as monitoring and control actions. Actions may include pre-conditions that must be met before they can be executed, as well as expected post conditions that are monitored to ensure that the command has executed and had the desired outcome. Declarative knowledge is the information that is required to correctly operate the system but which is not necessarily directly related to the execution of control actions.
Declarative knowledge includes sequence and timing constraints and performance requirements.
The activity planner uses system knowledge to augment semantic control actions comprising the activity plan with system-specific control syntax. The activity plan is then posted on the blackboard for use by the control executive. The blackboard is a hierarchical dynamic data structure on which the planner and control executive post evolving expectations, system state information, and the results of the execution of control actions. The proposed blackboard integrates three major data structures. The activity plan , is largely static.