We describe briefly an implemented example that illustrates the use of CYPRESS within a military operations domain. This domain is an extended version of the one used for the second Intergrated Feasibility Demonstration in the ARPA-Rome Laboratory Planning Initiative. The domain knowledge includes approximately 100 plan operators, 500 objects with 15-20 properties per object, and 2200 initial predicate instances. Plans range in size from several dozen to 200 actions, usually spread among numerous parallel threads of activity .
The scenario begins with a goal request for deterring several military threats. SIPE-2 is invoked to produce a plan using a set of ACTs previously input to the system. During the planning process, Gister-CL is used to assist SIPE-2 in choosing appropriate military forces for particular missions.
The plan produced by SIPE-2 contains four main threads of parallel activities: two threads for deterrence using ground forces, one for deterrence using naval forces, and the fourth using air forces. Throughout the planning process, PRS-CL monitors the world for additional goals and events that might require immediate action. PRS-CL executes the plan by applying appropriate ACTs to refine the plan to lower-levels of abstractions, eventually bottoming out in actions that are executable in the world. PRS-CL remains responsive to new goals and events throughout.
As part of the air deterrence operations, aircraft are moved among various air bases. The use of an air base requires explicit transit approval, which is granted initially for all bases in the domain. An execution failure can be triggered by rescinding transit approval for any of the bases used in the plan. The PRS application agent records any such changes, and detects a failure when execution reaches the stage where the rescinded approval is required. There are no ACTs defined for repairing such a failure locally, thus execution would completely fail at this point without replanning. When replanning is enabled, the application agent will notify the Replanner agent, which in turn will issue a replanning request to SIPE-2. Meanwhile, execution of the remaining branches of the original plan continues without disruption.
Replanning for this situation produces a modified plan in which an alternative mobilization strategy is employed. One of our test cases results in the removal of a dozen actions from the plan, replacing them with a new subplan of similar length. The operations in the new plan are selected so as not to interfere with the continuing execution of actions on other parallel threads in the original plan. The new plan is sent to to the PRS application agent, which integrates the new plan with its current activities and continues.