MYCIN example

1
MYCIN example

• Joe passing

2
Description

• If the preparation for the exam is good and the
  student slept well, then there is a good chance
  (0.7) that the student will pass the exam
• If the students contribution to the team effort
  is high and the workload of the student is low,
  then there is a good chance (0.8) that the
  student will pass the exam.
• If the workload of the student is high and the
  extra-curricular activities are high, then there
  is a good chance (0.6) that the student will fail
  the exam.
• If the extra-curricular activities of the student
  are low and the health of the student is good,
  then there is a good chance (0.6) that the
  student will pass the exam.

3
Rules/Interpretations

• (e1) Preparation(X,good) Sleep(X,well) ?1
  Pass(X) I(e1) 0.7
• (e2) TeamContrib(X,high) Workload(X,low) ?2
  Pass(X) I(e2) 0.8
• (e3) Workload(X,high) ExtraAct(X,high) ?3
  Pass(X)I(e3) 0.6
• (e4) ExtraAct(X,low) Health(X,good) ?4
  Pass(X)
• I(e4) 0.6
• I(Preparation(Joe,good)) 0.7
• I(Sleep(Joe,well)) 0.6
• I(TeamContrib(Joe,high)) 0.9
• I(Workload(Joe,low)) 0.6
• I(ExtraAct(Joe,high)) 0.3
• I(Health(Joe,good)) 0.8

4
Question

• We want to interpret the statementJoe passes
  the exam
• equivalent to Pass(Joe)
• need to compute measure of belief (MB) and
  measure of disbelief (MD) of Pass(Joe)
• Note range of MB and MD is 0,1 but they are
  not probabilities thus MB 1-MD (not
  necessarily)
• range of the interpretation values I is -1,1
  where 0 is neutral, 1 is strongly agree and -1 is
  strongly disagree
• Note because of lack of initial knowledge in the
  system, we will treat the input Is as
  probabilistic entities thus adding up to 1 for
  each object we also assume they are initially
  positive

5
Answer (MD)

• MD(Pass(Joe),e) MD(Pass(Joe),e3) I(e3)
  max0,minI(Workload(Joe,high)),
  I(ExtraAct(Joe,high)) 0.6 max0, min1-0.6,
  0.3 0.60.3 0.18

6
Answer (MB)

• MB(Pass(Joe),e1) I(e1) max0,minI(Prepara
  tion(Joe,good)), I(Sleep(Joe, well)) 0.7 0.6
  0.42
• MB(Pass(Joe),e2) I(e2) max0,minI(TeamCon
  trib(Joe,high)), I(Workload(Joe, low)) 0.8
  0.6 0.48
• MB(Pass(Joe),e4) I(e4) max0,minI(
  ExtraAct(Joe,low)), I( Health(Joe, good)) 0.6
  0.7 0.42
• MB(Pass(Joe),e2,e4) MB(Pass(Joe),e2)
  MB(Pass(Joe),e4)(1-MB(Pass(Joe),e2))
  0.480.420.520.7
• MB(Pass(Joe),e) MB(Pass(Joe),e1,e2,e4)
  MB(Pass(Joe),e1) MB(Pass(Joe),e2,e4)(1-MB
  (Pass(Joe),e1)) 0.420.70.580.83

7
Answer (I)

• I(Pass(Joe)) MB(Pass(Joe)) MD(Pass(Joe))
  0.83 0.18 0.65
• So, based on our knowledge, Joe passes the exam
  with interpretation value of 0.65.