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Select Parameter Inference

P&R is characterized as a parametric design task whose goal is to assign values to each parameter in a system. The select parameter inference chooses one parameter among all the parameters to compute its value. Figure 3 shows the inference with its knowledge roles: INPUT PARAMETERS, PARAMETER DEPENDENCY RELATIONS and SELECTED PARAMETER.

The INPUT PARAMETERS must be supplied by the user before the system is configured. In the VT task, the input parameter values provide the basic characteristics of the elevator system such as door opening type (center, for doors which open in the center; side, for doors which open to one side of the car), car capacity (the maximum occupant weight that the system is able to support) and so on. The input parameter values are used as a starting point for computing the values of the other parameters.

The PARAMETER DEPENDENCY RELATIONS define how the values of some parameters depend on the values of other parameters to be computed. In the VT task, for example, the sling underbeam is equal to the car cab height plus the sling underbeam space. This formula expresses that the sling underbeam depends on the car cab height and the sling underbeam space. The dependency relations among the parameters are a fundamental aspect of the knowledge structure for Propose&Revise. Here, instead of a hierarchical structure of components and subcomponents, the parameters are organized in a network that models the interdependencies among parameters. Thus, to use Propose&Revise, the application domain must present or must be mapped to the same organization. In this way, some assumptions are made about the dependency relations among parameters:

• A parameter p1 depends on a parameter p2, if p2 is used to compute the value of p1.
• A parameter p1 depends indirectly on a parameter p3, if p1 depends on p2 and p2 depends directly or indirectly on p3.
• An input parameter p1 does not depend on other parameters.

In addition, it cannot exist cycles in the dependency relations:

• If a parameter p1 depends on parameter p2, p2 does not depend on p1.
• If a parameter p1 depends indirectly on p3, then p1 does not depends on p3.

Figure 5: The formalization of the select parameter inference and its knowledge roles.

The PARAMETER VALUES are supplied by the user for the input parameters, or they can be the values of the other parameters computed by the method. In P&R, each parameter has a unique value. The SELECTED PARAMETER has its value not computed yet, but all parameters on which it depends are already computed.

Figure 5 presents the formalization of the select parameter inference and its knowledge roles. In (1){ the class of parameters is defined. Definition (2) associates a unique value to each parameter. The value-cardinality of frame ontology constrains the relation Parameter-Value in such a way that each parameter has a unique value. In (3) the input parameters are defined. Definition (4) expresses the direct dependency relations among parameters. Here, an input parameter does not depend on another parameter. In (5), the Depends-On relations comprise the direct and indirect dependencies among parameters. In addition, the definition makes explicit the fact that no cycles exist in the dependency relations. The ASYMMETRIC-RELATION and WEAK-TRANSITIVE-RELATION are defined in frame ontology. The ASYMMETRIC-RELATION means that if ?p1 depends on parameter ?p2, this implies that ?p2 does not depend on parameter ?p1, such that there are no cycles in the direct dependency relations. To define the indirect dependency among parameters, the WEAK-TRANSITIVE-RELATION says that, if a parameter ?p1 depends on parameter ?p2, and that ?p2 depends on parameter ?p3, then ?p1 depends on ?p3. It is a ``weak'' transitive relation because ?p1 is not equal to ?p3, which warrants the nonexistence of cycles in the indirect dependency relations. In (6), the output knowledge role is defined. Definition (7) presents the select parameter inference that chooses a parameter whose value is not computed yet, but all parameters on which it depends are already computed.

Next: Propose Inference Up: METHOD ONTOLOGY FOR Previous: METHOD ONTOLOGY FOR

Eliana Coelho
Wed Sep 4 15:57:17 EDT 1996