Accessing information both via a hierarchy of situations and explicit relationships among them requires a computational mechanism. Given an infon and a situation s , this relation holds if is made true by s , i.e., s . They are neither nomic nor necessary, i.e., they can be violated. All types of constraints can be conditional and unconditional . Conditional constraints can be applied to situations that fulfill some condition while unconditional constraints can be applied to all situations.
Constraints enable one situation to provide information about another and serve as links.
Constraints can be used as inference rules in a computational system. When viewed as a backward-chaining rule, a constraint can provide a channel for information flow between types of situations, from the antecedent to the consequent. Another way of viewing a constraint is as a forward-chaining rule. This approach enables an agent to alter its environment.