Overview

You will develop a series of search heuristics for solving planning problems. These heuristics will be demonstrated using the Blocks World domain, in addition to two domains of your own making.

Setup

• Place planner.zip inside your project directory from Project 1, and unzip the file.
• Click on your project in the package explorer, and press F5 to refresh.
• The files should now be there.

Programming Assignment

• planner.heuristics
  • BreadthFirst.java will implement breadth-first search.
  • You will place additional heuristics here as you create them.
  • Every heuristic in this package will be visible to PlanViewer.java.
• planner.core
  • Action.java: Describes a plan operator.
  • BasicPlanner.java: Wraps a BestFirstSearcher for generating a plan. It is abstract in order to enable variants to handle different BestFirstObject classes. Implements the Planner interface.
  • BasicPlanStep.java: Useful basis for creating BestFirstObject classes.
  • BestFirstPlanner.java: Extends BasicPlanner. When provided with a BestFirstHeuristic, the result is a functioning planner.
  • BreadthFirstTest.java: Should pass all tests upon downloading.
  • Conjunction.java: Represents the effects of an Action.
  • Domain.java: Represents a planning domain.
  • Plan.java: Represents a plan.
  • PlanGraph.java: Represents a plan graph, a data structure that can be useful to assist in creating plans. You will complete the extractNoDeletePlan() method.
  • PlanGraphTest.java: Unit test for PlanGraph. It will fail initially. It should pass once your solution to PlanGraph.java is complete.
  • PlanStep.java: Represents a plan step, for use in the search process.
  • Planner.java: Interface for planners. Implemented by BasicPlanner.
  • Predicate.java: Represents a parameterizable true/false statement.
  • Problem.java: Represents a specific planning problem in a given Domain.
  • State.java: Collection of Predicate objects representing the state of the world.
• planner.gui
  • PlanViewer.java: Runnable GUI for evaluating your planning heuristics.
• planner.lisp: The files in this package you may safely ignore.

• A heuristic that counts the number of goals that have not yet been achieved.
• For each domain:
  • Develop at least one heuristic that uses properties of the domain. For example, in the blocks world, a heuristic could count the number of blocks stacked atop a block that needs to be moved as part of its calculation.
• Create a heuristic that creates a relaxed plan that solves the problem. This relaxed plan will ignore the delete effects of each Action. To find a relaxed plan, complete the extractNoDeletePlan() method in the PlanGraph class. Then use the length of the relaxed plan as the estimate.
• Devise at least one additional heuristic. It may be domain-independent, or it may be specialized to one of the three domains you are employing.

Domains

• The first domain should represent a robot delivering packages in an office building.
• The second domain can represent any environment you would like to encode.
• When creating your three problems, try to create at least one problem that you believe will be difficult for the planners to solve.

Experiments

Note: If your planner can solve all of the regular Blocks World problems, some extra-hard problems are available in the blocks2 directory.

For each experiment you run, record:

• Nodes expanded
• Maximum depth
• Effective branching factor
• Solution length
• Time (milliseconds)
• ms/node expansion

Paper

When you are finished with your experiments, you will write a short paper summarizing your findings. Include the following details in your paper:

• A description of each heuristic
• The data you collected from each of your experiments
• An analysis of the data, including:
  • A discussion of the relative merits of the heuristics relative to breadth-first search and each other
  • An analysis of how the heuristics are affected in different ways by different domains
  • The degree to which the results matched your expectations
• Copies of the code for your heuristics

Deadlines

• On Tuesday, September 5, come to class with a two-slide PowerPoint presentation. On the first slide, describe one domain you have created. On the second slide, briefly describe the heuristics you have already implemented, in addition to other possibilities you are considering.
• Submit your paper and code by 1:15 pm on Thursday, September 7.

Grading criteria