DOC PREVIEW
MIT 6 871 - Lecture Notes

This preview shows page 1-2 out of 6 pages.

Save
View full document
View full document
Premium Document
Do you want full access? Go Premium and unlock all 6 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 6 pages.
Access to all documents
Download any document
Ad free experience
Premium Document
Do you want full access? Go Premium and unlock all 6 pages.
Access to all documents
Download any document
Ad free experience

Unformatted text preview:

687.1 Lecture 6 1Rule-Based Systems6.871-- Lecture 66.871 - Lecture 6 1Outline MYCIN– Introduction»Task» Sample Interaction» Reasons for Success– How It Worked» Knowledge Representation» Architecture and Control Structure» Inexact Inference» Explanation» Interaction Help– Reasons for Success Revisited– Contributions Prospector “Rules Glasses”6.871 - Lecture 6 2MYCIN What was the task?– Medical diagnosis and therapy selection for bacterial infections of the blood Why this domain?– Overuse of antibiotics6.871 - Lecture 6 4Why This Domain Overuse of antibiotics Irrational use of antibiotics Maldistribution of expertise Domain is “small” and “isolated”6.871 - Lecture 6 5---------PATIENT-248----------1) Patient’s name: (first-last)** CR2) Sex:** MALE3) Age:** 524) Have you been able to obtain positive microbiological information about a possible infection of C.R.?** YES----------INFECTION--------------5) What is the infection?** ENDARTERITISSample Interaction: Clinical Data6.871 - Lecture 6 6The first significant organism from this blood culture (CULTURE-1)will be referred to as:--------------ORGANISM-1-----------------6) Enter the identity of ORGANISM-1** UNKNOWN7) Is ORGANISM-1 a rod or coccus (etc.):** ROD8) The gram stain of ORGANISM-1** GRAMNEG9) HAVE THERE BEEN positive cultures yielding organismsabout which you will NOT be seeking advice?** YESSample Interaction (cont’d)687.1 Lecture 6 26.871 - Lecture 6 79) Enter the identity of ORGANISM-2:** SALMONELLA (.4) E.COLI (.3)Sample Interaction (cont’d)6.871 - Lecture 6 8Is the patient’s illness with ORGANISM-1 a hospital-acquired infection?** WHY[i.e. WHY is it important to determine whether or not the infection with ORGANISM-1 was acquired while the patient was hospitalized][2.0] This will aid in determining the identity of ORGANISM-1.It has already been established that[2.1] the morphology of ORGANISM-1 is rod[2.2] the gram stain of ORGANISM-1 is gramneg[2.3] the aerobicity of ORGANISM-1 is faculTherefore, if[2.4] the infection with ORGANISM-1 was acquired while the patient was hospitalizedthenthere is weakly suggestive evidence (.2) that the identity of ORGANISM-1 is pseudomonas [RULE050]Sample Interaction: Explanation6.871 - Lecture 6 9INFECTION-1 is ENDARTERITIS with BACTEREMIA<Item 1> E. COLI <Item 2> SALMONELLA (species unknown)<Item 3> KLEBSIELLA-PNEUMONIAE<Item 4> PSEUDOMONAS-AERUGINOSA <Item 5> ENTEROBACTER<Item 6> PROTEUS-NON-MIRABILUSSample Interaction: Diagnosis6.871 - Lecture 6 10[REC 1] My preferred therapy recommendation is as follows:In order to cover for Items <1 3 4 5 6 >:Give: GENTAMICINDose:128 mg (1.7. Mg/kg) q8h IV (or IM) for 10 daysComments: Modify dose in renal failureIn order to cover for Item <2>:Give: CHLORAMPHENICOLDose:563 mg (7.5 mg.kg) q6h for 14 daysComments: Monitor patient’s white countDo you wish to see the next choice therapy?** NOSample Interaction: Therapy6.871 - Lecture 6 11How It Worked: RepresentationRule 27If: 1)the gram stain of the organism is gram negative, and2)the morphology of the organism is rod, and3)the aerobicity of the organism is anaerobic,Then:There is suggestive evidence (.7) that the identity of the organism is Bacteriodes.6.871 - Lecture 6 14INFERENCE ENGINEKNOWLEDGEBASEArchitecture687.1 Lecture 6 36.871 - Lecture 6 15IDENTITY = BacteroidesGRAM MORPHOLOGY AEROBICITYRule 27Control Structure…Rule 1546.871 - Lecture 6 16Control Structure What kind of search?– Backward-chaining, depth-first With what variations?– Generalized subgoalsE.g. “determine identity”, not “is identity = E.coli”– Every rule relevant to goal is explored– Inexact inference6.871 - Lecture 6 17R1: A and B X (.4)R2: C and D X (.3)A and B and C and D ?Inexact Inference Desiderata:– Commutative–Asymptotic– Balances positive and negative evidence6.871 - Lecture 6 18R1: A and B X (.4)R2: C and D X (.3)A and B and C and D ?Inexact Inference “increase certainty .3 more from current value”X(.4 + .3(1 - .4)) = X(.58)current value remaining uncertaintynew valueA and B X (.4)C and D:6.871 - Lecture 6 19R1: A (.5) and B (.6) X (.4)R2: C (.4) and D (.7) X (.3)A and B and C and D ?Inexact Inference AND: min (A and B) = .5min (C and D) = .4R1: .5 * .4 = .2R2: .4 * .3 = .12Combining: .2 + .12( 1 - .2) = .30current valueremaining uncertaintynew value6.871 - Lecture 6 20** HOW DID YOU DECIDE THAT ORGANISM-1 WAS AN E.COLI?I used rule084 to conclude that the identity of ORGANISM-1 is e.coli. This gave a cumulative c.f. of (.51).I used rule003 to conclude that the identity of ORGANISM-1 is e.coli. This gave a cumulative c.f. of (.43).Explanation687.1 Lecture 6 46.871 - Lecture 6 21** WHY DIDN’T YOU THINK THAT ORGANISM-1 WAS NEISSERIA?The following rules could have been used to determine that the identity of ORGANISM-1 is neisseria: 9.However, none of these succeeded in the context of ORGANISM-1. If you would like an explanation for why any of these rules failed, please enter their numbers:** 9Clause 2 of rule009 [“the morphology of the organism is coccus”] was already known to be false for ORGANISM-1, so the rule was never tried.Explanation6.871 - Lecture 6 22Successful? Appropriate task: Narrow domain, heuristic knowledge, articulate experts, etc. The match of knowledge and representation:– Knowledge about of how the body works, vs.– Knowledge about how to diagnose it Answer was a ranked list, not a single result Perhaps most important:Having the right abstractions, the right language6.871 - Lecture 6 23The Right AbstractionIf …the organism is gram-negative, andthe portal of entryis skin-wound,Then the organism is likely to be … It’s an abstraction It’s the right abstraction for this task Where did it come from?6.871 - Lecture 6 24What ought a rule to be?Answer:An independentsingle-stepinferentialempirical association.6.871 - Lecture 6 25What ought a rule to be? Independent– Does it make sense in isolation? Single step: mental hygiene Inferential: focus on the knowledge level Empirical association– Association: symptom & disease– Empirical: noticed but not understood– Logic-like, but:»Inexact» Not truth-preserving6.871 - Lecture 6 26What Ought a Rule to Be?IF There is pressure on project leader, Respondent is R&D manager,No increase in growth


View Full Document

MIT 6 871 - Lecture Notes

Download Lecture Notes
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view Lecture Notes and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Lecture Notes 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?