This is the 2007 version. Click here for the 2017 chapter 07 table of contents.

Constraint Satisfaction as a Problem-Solving Approach

Sometimes a problem is not embedded in a long set of action sequences but requires picking the best option from available choices. A good general-purpose problem solving technique is to list the constraints of a situation (either negative constraints, like limitations, or positive elements that you want in the final solution). Then pick the choice that satisfies most of the constraints.

For example, in landscaping around a house, you might identify these elements:

How can constraint satisfaction be employed as a general problem solving technique?

1. The grass, trees, or bushes should be hardy in your climate. You do not want them dying after a few years.

2. The plants should not be too expensive, if you are on a budget.

3. The trees and bushes should not require too much care, if you are not spending all your time gardening or working in the yard.

4. Any trees you put in should shade the house during the summer (especially if you live in a warm climate) or let sun through in the winter (especially if you are in a cold climate) or they should perform some other function such as looking attractive, aiding privacy, or providing fruit or nuts.

As you evaluate landscaping alternatives, you run through your checklist and see which of the available plantings would meet a large number of important constraints. A solution that satisfies a large number of constraints simultaneously is likely to be esthetically pleasing. It will seem like an elegant solution, in its own small way, and it will be satisfying.

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