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5.1 Propose

The propose step proposes a configuration. It has to propose an instance of the general schema that we use for representing PSMs. In our study such a proposed configuration is an instantiation of the six components of the diagnostic schema. We describe a method by a termgif

ds(Obs-mapping,Vocabulary,Cover,NotContra ,Selection,Solform)

where each argument of ds (for: diagnostic system) represents a definition of the particular component (e.g. Obs-mapping, ie. one of the underlined terms from formula (1)). Such a definition is a definition taken from the possible set of instances of a component. The proposed components definitions are not structured, but are only a definition from a fixed set that is given beforehand. The Selection component is the sole component that can be structured. However in the propose step only ``basic'' selection criteria are proposed, which can be adapted to more complex ones later in the modify step the Slection component. We will illustrate this in the scenario in Section 6.

The propose step (see Figure 3) results in a configuration (i.e. a method description) from the possible configuration space, by selecting a definition for each of the six components. This selection is controlled by the required static goals. An example of a static goal would be that the configured method has to result in a small set of the solutions, which would result in proposing a strong Selection component.

If the static goals do not determine a definition for each component (or when there are no static goals), the proposed method is completed with an arbitrarily chosen definition from the set of possible definitions for these components. When different static goals require different definitions of the same component, one of these definitions is chosen arbitrarily, and the goals that are not guaranteed by the method become dynamic goals. Satisfying static goals might depend on the diagnostic problem or on the given assumptions. For this reason, the given input assumption and problem are input for the propose step.

Characteristic of this propose step is that it always gives a proposal, and that the static goals control the search space in this phase of the configuration process. The specific (diagnostic) knowledge that is used in the propose step is (1) the knowledge for fulfilling a static goal, (2) the number of components (the arity of the schema of ds(...)) (3) a set of definitions for each component. The propose step enables us to generate possible methods using the definitions for the diagnostic components in the system. However, at this moment we do not say anything about the sequence of choices of diagnostic component and about the sequence of the proposed configurations.

Figure 3: Propose Step: The Possible Method is a complete definition of a method, where the Goals are fulfilled as much as possible. The Dynamic Goals are those goals which are part of the Goals, but which are not guaranteed by the proposed method.

next up previous
Next: 5.2 Verify Up: 5 A Propose-critique-modify Method Previous: 5 A Propose-critique-modify Method

Frank van Harmelen
Fri Oct 4 13:40:35 MET DST 1996