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Artificial Intelligence and Soft Computing: Behavioral ... - Arteimi.info

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multiple expert responses. The main problem here is to measure the<br />

consistency among the experts, often called inter-observer reliability. The<br />

‘inter-class correlation co-efficient’ is a common measure for consistency<br />

among the experts. After a correlation co-efficient is estimated, we can use a<br />

related statistic to compare the joint expert agreement with the system [4]. If<br />

the experts’ opinions are categorical variables like good, average, poor, etc.,<br />

rather than continuous variables, Kappa statistics may be used to measure<br />

their composite reliability <strong>and</strong> then a related statistic to compare their joint<br />

agreement with the system agreement [4].<br />

21.3 Verification of Knowledge Based System<br />

Errors creep into knowledge based systems in various stages. First during<br />

knowledge acquisition phase, experts miss many points to highlight to the<br />

knowledge engineers. Secondly, the knowledge engineer misinterprets the<br />

expert’s concept <strong>and</strong> encodes the semantics of expert’s concept incorrectly.<br />

Thirdly, there is a scope of programming error. Lastly, as the knowledge base<br />

is developed in incremental fashion over several years, the entry of<br />

inconsistency, redundancy <strong>and</strong> self-referencing (circularity) in the knowledge<br />

base cannot be ignored. The knowledge base of an expert system, thus, needs<br />

to be verified before it is used in commercial expert systems.<br />

Graph theoretic approaches [9-10] have been adopted for eliminating<br />

various forms of shortcomings from the knowledge-base. One such well-<br />

known graph is the Petri net, which has already been successfully used in<br />

knowledge engineering for dealing with imprecision of data <strong>and</strong> uncertainty<br />

of knowledge. In this section, we will use Petri nets for verification of<br />

knowledge base. It may be noted that various models of Petri nets are being<br />

used in knowledge engineering, depending on the type of application. The<br />

model of Petri nets that we will use here is an extension of the model<br />

presented in chapter 8. For the sake of convenience of the readers, we<br />

represent a set of knowledge by a Petri net (fig. 21.6).<br />

Knowledge base:<br />

1. Ancestor (X, Y) ← Parent (X,Y).<br />

2. Ancestor (X, Y) ← Parent (X,Z), Ancestor (Z,Y).<br />

3. Parent (d, j).<br />

4. Parent (j, m).<br />

The Petri net shown in fig. 21.6 consists of a set of places P, a set of<br />

transitions Tr, arc functions A <strong>and</strong> two tokens at place p2, given by

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