Chapter 15 - People

More documents

Recommendations

Info

374 NEOMYCIN: Reconfiguring an Expert System for Application to TeachingHaving exhausted its limited knowledge, the program finds no other relevant, hypothesis-oriented questionsto ask. Several general questions are asked ....11) Is Mike receiving any medications?•• NORepeating EHS loop: focus = COCCIDIOIDEStask RULE430 succeeded.12) Has Mike been recently hospitalized?•• NORepeating EHS loop: focus = COCCIDIOIDESIf additional data had been supplied, new hypotheses might have been placed on the differential andstrategies for grouping or refining might have been called into play once again. This ends the history-takingprocess. Next the program would order laboratory tests, process them, and perhaps return to gatheringcircumstantial evidence.FIGURE 15-4 continued15.4 The Diagnostic Meta-StrategyFormalizing the diagnostic strategy from protocol analysis was the mostdifficult part of designing NEOMYCIN. Figure 15-5 shows the generaloutline of the meta-strategy. Each nonterminal node in the tree stands fora task that is achieved by a set of rules. An important aspect of our modelof diagnosis is that the process can be taught as a task-posing activity: theproblem solver thinks in terms of what he or she is trying to do (e.g., toconsider unusual causes and so broaden the differential) in order to bringknowledge sources to mind. Thus the meta-strategy is structured so thetasks make sense as things that experts try to do.Figure 15-5 shows that the main object of the meta-strategy is to decidewhat data to collect next (invoke MYCIN's FINDOUT routine), generallyby focusing on some hypothesis in the differential. Aside from collectinginitial information, the basic idea is that collecting circumstantial evidenceis a process of establishing the hypothesis space. This process takes the formof considering what could cause the reported data, grouping and refiningthe differential, and asking general questions. 3 A great deal of what wemight call heuristic confidence is placed in the general questions, which constitutethe outline of the "history-taking process" as it is generally taughtto medical students. However, strategies for using causal and disease processknowledge enable the expert to be an efficient problem solver in acombinatorially large space, and these strategies are generally not taught.3Group and differentiate is used here in the loose sense of establishing general focus on a processthat is consistent with hypotheses suggested independently by the data. Clustering (in multipleways) and discriminating, the usual meaning of the term, is one operation for achieving thisfocus.
The Diagnostic Meta-Strategy 375Make-diagnosis [384]Establish-hypothesis-spaceProcess-hard-data[rules]initialinfochiefcomplaint~&drre~not compact[393]process split[397]top unexplored[400]'--------- ~Pu rsue-hypothesis~\~skipped-evidence[409]trigger\. [410]enabling[411]~Findout[5 rules]Jother[431].1FIGURE 15-5 NEOMYCIN's diagnostic meta-strategy. (Rulenumbers in brackets appear in the sample trace.)The implementation is in terms of hierarchical meta-rules,4 which asa whole constitute the meta-strategy_ Figure 15-6 illustrates how the rulesfor a given task are treated as a pure production system-they are repeat-4S0 called because they indirectly control the invocation of the domain-dependent objectrules. Davis's conception of meta-rules was that they would directly order object-level rules.However, in our theory of diagnostic strategy, meta-rules reason about the state of the differentialand knowledge sources (kinds of evidence) that could change it in desirable ways.Thus, our meta-rules choose kinds of object rules (hypothesis-confirming, process-oriented,ca~sal).
Page 1 and 2: 15NEOMYCIN:. Reconfiguring a Rule-B
Page 3 and 4: Introduction 363• representations
Page 5 and 6: Introduction 365IF: 1) The infectio
Page 7 and 8: An Overview of NEOMYCIN 367trigger
Page 9 and 10: A Sample Case 369METARULE397 (for t
Page 11 and 12: A Sample Case 371Differential:repla
Page 13: A Sample Case 373Repeating E&R loop
Page 17 and 18: Etiological Taxonomy, Causal and Di
Page 19 and 20: Some Limitations 37915 • 6Related
Page 21: Future Research 381system. This is

Chapter 15 - People

Create successful ePaper yourself

Delete template?

Save as template?