STRIPS Architecture

STRIPS was the architecture used by the robot Shakey that implemented the deliberative paradigm, which used a mean-ends analysis technique:

• If the goal is at “action” away, perform it and end.
• If not, select the action that reduces the difference between the current status and the desired status (end goal).

STRIPS uses recursion to identify why the goal cannot be achieved (a precondition) and sets this as a new goal. Then, try to achieve this goal. When a goal is achieved, the action associated is added to a list, which all of them will make for the plan to perform.

STRIPS needs that the designer identifies and implements the following terms:

• A world model representation.
• A difference table, which will have some preconditions, some operators, an add and a delete list (they update the state and conditions of the world).
• A difference evaluator function.

The steps of the algorithm are: 1. Compute the difference between the initial state and the end state, and if no difference, end. 2. If there is difference, reduce the difference by selecting the first operator of the list that reduces this difference, which is expressed on the add-list. 3. If there are some preconditions that are not met, take the first one as the new goal by pushing it to a stack, and recursively reduce the difference performing 2-3. 4. When all preconditions are met, push the operator to the plan stack and update the world model. Return the operator that failed so the recursion goes on.

Notes References

20210711201454 Robotics Basics - Deliberative Paradigm

20210514183815 INDEX - Robotics

References

(Murphy 2000)

Murphy, Robin. 2000. Introduction to AI Robotics. Intelligent Robotics and Autonomous Agents. Cambridge, Mass: MIT Press.