Constraints are a natural means of knowledge representation in many disparate fields. A constraint often takes the form of an equation or inequality, but in the most abstract sense is simply a logical relation among several variables expressing a set of admissible value combinations. The following are simple examples: the sum of two variables must equal 30; no two adjacent countries on the map may be coloured the same; the helicopter is designed to carry only one passenger, although a second can be carried in an emergency; the maths class must be scheduled between 9 and 11am, but it may be moved to the afternoon later in the term. It is this generality and simplicity of structure which underly the ubiquity of the constraint-based representation in Artificial Intelligence.
KeywordsConstraint Satisfaction Constraint Satisfaction Problem Search Effort Hierarchical Decomposition Flexible Planning
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