After computing the values of the parameters, P&R verifies that the values satisfy the constraints associated with the parameters. The check inference examines the constraints whose parameters are already computed, and all the parameters on which they depend have been already computed. Figure 3 illustrates the inference and its knowledge roles: PARAMETER VALUES, CONSTRAINT PROCEDURES, CONSTRAINT DEPENDENCY RELATIONS and CONSTRAINT RESULTS.
The constraints limit the values of some parameters. These constraints are evaluated after the PARAMETER VALUES are computed. Not all parameters have constraints, and some parameters may have more than one constraint. In the VT task, for instance, the parameter car overtravel has two constraints, a constraint that limits its maximum value, and another one that limits its minimum value.
The CONSTRAINT PROCEDURES are procedures that evaluate if the constraint is satisfied. The constraints establish DEPENDENCY RELATIONS among the parameters. Each procedure contains one expression that computes the CONSTRAINT RESULTS, that can be ``true'' (if the constraint is satisfied) or ``false'' (if the constraint is not satisfied). In the VT example, the parameter car overtravel has the constraint minimum car overtravel, which has a procedure that evaluates if the value of car overtravel is at least the counterweight runby plus 1.5 times the counterweight buffer stroke plus 24 inches. This constraint depends on the value of the parameters car overtravel, counterweight runby and counterweight buffer stroke.
Figure 7: The formalization of the check inference and its knowledge roles.
Figure 7 shows the formalization of the
check inference and its knowledge roles. The (11)-(14)
definitions specify the knowledge roles for the inference. In (16),
the check inference verifies the constraints whose
parameters have their values already computed, and have all the
parameters on which they depend already computed.