MIT 6 872 - Decision Support via Expert Systems (50 pages)

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Decision Support via Expert Systems



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Decision Support via Expert Systems

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Pages:
50
School:
Massachusetts Institute of Technology
Course:
6 872 - Biomedical Computing

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Decision Support via Expert Systems 6 872 HST950 Peter Szolovits Components of an Expert System Knowledge In various forms associations models etc Strategy Baconian exhaustive enumeration on line etc Implementation Programs pattern matching rules etc Flowchart BI Lincoln Labs Clinical Protocols 1978 Codifying Human Knowledge Decomposition into chunks of knowledge chaining of inferences Matching of case data to prototypical situations Using causal models pathophysiology to figure out cases Mycin Rule based Systems Task Diagnosis and prescription for bacterial infections of the blood and later meningitis Method RULE037 Collection of modular IF the organism rules 1 stains grampos 2 has coccus Backward chaining shape Certainty factors 3 grows in chains THEN There is suggestive evidence 7 that the identity of the organism is streptococcus Mycin consult PATIENT 1 1 Patient s name FRED SMITH 2 Sex MALE 3 Age 55 4 Have you been able to obtain positive cultures from a site at which Fred Smith has an infection YES INFECTION 1 5 What is the infection PRIMARY BACTEREMIA 6 Please give the date when signs of INFECTION 1 appeared 5 5 75 The most recent positive culture associated with the primarybacteremia will be referred to as CULTURE 1 7 From what site was the specimen for CULTURE 1 taken BLOOD 8 Please give the date when this culture was obtained 5 9 75 The rst signi cant organism from this blood culture will be called ORGANISM 1 9 Enter the identity of ORGANISM 1 UNKNOWN 10 Is ORGANISM 1 a rod or coccus etc ROD 11 The gram stain of ORGANISM 1 GRAMNEG Davis et al Arti cial Intelligence 8 15 45 1977 How Mycin Works To find out a fact If there are rules that can conclude it try them Ask the user To run a rule Try to find out if the facts in the premises are true If they all are then assert the conclusion s with a suitable certainty Backward chaining from goal to given facts Dynamically traces out behavior of what might be a flowchart Information used everywhere appropriate



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