Click here for the derivation of the solution to the Sussman Anomaly.

SIPE-2: System for Interactive Planning and Execution

David E. Wilkins

AI Center , SRI International

See a 7-minute video, recorded in 2013, giving a historical overview of the SIPE HTN planning system (expand window to be at least 1280x720).


The key features of the SIPE-2 plan-generation technology are:



Artificial Intelligence (AI) planning techniques developed over the past three decades at the AI Center of SRI International have now reached the point where they can impact real problems. SIPE-2 is the most advanced of SRI's plan generation and execution systems, and has been employed by numerous users to solve a range of interesting problems, as described above. It is the planner in the Cypress and CPEF systems and is used in the Multiagent Planning Architecture.

SIPE-2 is a performance-oriented, general-purpose software system for generating and monitoring the execution of plans. It plans hierarchically, using different levels of abstraction, and provides a formalism for describing actions as operators. Given an arbitrary initial situation and a set of goals, SIPE-2 either automatically or under interactive control combines operators to generate plans to achieve the prescribed goals in the given world. In contrast to most AI planning research, heuristic adequacy (efficiency) has been one of the primary goals in the design of SIPE-2, which includes many heuristics for reducing computational complexity. Unlike expert systems, the SIPE-2 architecture is capable of generating a novel sequence of actions that responds precisely to the situation at hand.

Planning requires the system to predict how the world will change as actions are performed. However, in real-world domains, things do not always proceed as planned and it becomes increasingly important to use as much as possible of the old plan when new situations arise. SIPE-2 has execution-monitoring techniques that accept new information about the world and modify the plan minimally to respond to unexpected events.

Human-Computer Interface

In practical applications, natural pictorial representations are necessary for a human user to understand the domain knowledge, the plan, the planning process, and the execution of the plan. SIPE-2 provides a powerful graphical user interface (built on Grasper-CL). The image at the top of this page is a pictorial representation of a plan drawn by SIPE-2. Graphical tools can be used for the following purposes:
  1. inputting domain knowledge and creating operators
  2. following and controlling the planning process
  3. viewing complex information (including plans, operators, and world descriptions) as graphs on the screen
SIPE-2 incorporates the Advisable Planner. The Advisable Planner enables users to direct the planning process in a more powerful and general manner, through the provision of high-level guidance that influences the nature of the solutions generated. Advice consists of task-specific properties of both the desired solution and the problem-solving process to be used for a particular problem. Advice is an adjunct to the domain knowledge that underlies a given planning application.

Using common knowledge bases in SIPE-2.

SIPE-2 Publications

Installing SIPE-2 at Your Site

SIPE-2 uses Tachyon for temporal reasoning.

SIPE-2 and Grasper-CL are trademarks of SRI International.

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Dr. David E. Wilkins
Last modified: Wed May 24 14:59:58 2000