1.1 Expert System

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Expert System

An EXPERT SYSTEM is a computerprogram that exhibits Expert Levelperformance in solving complex

problems.

1

Reasons with Facts about the World:

Combines General Facts/Rules (about Diseases, ...)

with Specific Facts (about Patient)

to Produce new Conclusion (diagnosis)


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Story

MD sees patient perhaps MENINGITIS! Performs standard tests

Calls Infection Disease (medical) expert

2

Dialogue: Expert asks for info re: patient

Fever, Organism Morphology, Gram Stain, Spinal Fluid,

Doctor's answers: D IRECT : from direct measurement, Lab tests Qua l i t a t i v e : Has HIGHfever Vague : Portal of Entry was GastroIntestinal (w/certainty 0.6) Un k n own : dont know identity of organism?


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Story cont

MD can ask questions: Why ask about portal of entry? Expert answers:

trying to showinfecting organism is ENTEROBACTERICAE

this information is crucial in that decision. If further questioned, point to definitive study

Expert provides DIAGNOSIS organism was one of {E.coli, Enterobacteria } suggest TREATMENT: Give GENTAMICIN

Happily ever after...

3


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The Catch

Expert System

4


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Medical Expert Systems

MYCIN

Blood Infections

CADUCEUS

Internal Medicine CASNET

Glaucoma

Present lllnessProgram

Kidney

5

Digitalis advisor Erratic Heartbeat

VM

Ventilator Management ALVEN Ventricle Movement

ONCOCIN

Cancer TreatmentProtocols


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Declarative Programming''

6

Knowledge Base

--- -- --- ---- --- - -- ---- - --- ------ -- --- --Facts about the world

-- ---- --- ---- ----- -- ----- -- ----- -- --- - -

1

Is true?

ProofProcedure

2

Yes No

Give Gentamycin?


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Advantages of Framework

Simply

Information is Modular

Easy to Build

Easy to Modify (Extend, Debug)

Capable of Explanation

Declarative

Re-use same info for different tasks

7

store truthsask for other truths


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Computers ManipulateSYMBOLS

Numbers

3, 5, ...

Addition, Multiplication, ...

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PropositionsD1 is an inverter''

Inverters flip bits''... Deduction, ...


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Simple Deduction

Socrates is a man.

If Socrates is a man,Then Socrates is mortal.

9

Socrates is mortal.

In general


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Example of Deduction

RULES FACTS

R1:IfSocrates is a Man,

Then Socrates is Mortal

o

o

o

F1: Socrates is a Man.

o o10

Socrates is Mortal(Goal)

Socrates is a Man(NewGoal)

R1

Knowled

geBa

se


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Example of Deduction, #2

RULES FACTS

R1:IfPlato is a Man,Then Plato is Mortal

R2:IfPlato is a Cat

Then Plato is Mortal.

R3:IfPlato purrs,

ThenPlato is a Cat.

oo

F3: Plato purrs.

o

o

o 11

Plato is Mortal

Plato is a Man

R1

Plato is a Cat

R2

Plato purrs

R3


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Example of Deduction, #3

RULES FACTS

R2:IfPlato is a Cat

Then Plato is Mortal. o

R9:IfAristotle is a human and Aristotle is male,

ThenAristotleis a man

o

o

o

F3:Aristotleis male.

o

F8:Aristotle is a human

o 12

Aristotle is a man

Aristotle is maleAristotleis a Human

R9


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Oversimplified Proof Process

1. If Goal = FACT

then DONE YES

Else

1. Goal = Then Part of Rule R

then Goal If Part ofR

13

i

ii+1

else DONE NO


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JustManipulating Symbols

Consider claim

This is Belgium.

based on proof

Today is Tuesday. If Today is Tuesday

Then This is Belgium.

This is Belgium

Conclusion iswrong!

Conclusion isONLY AS TRUE

as PREMISES

If Premises true,then Conclusion is.

Not fault of PROOFprocess

GIGO14


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Rules

R1: if(1) You have a Parking Permit & (2) This space is Permit-Parkable,

then You can park at this space.

R2: if(1) This space is a Parking Space & (2) Permit-Sign at this space &

(3) Current date is Acceptable,then This space is Permit-Parkable.

R3: if(1) Current time is 7am-Midnight & (2) This space is Permit-Parkable,


R4: if (1) Current month is Dec-Mar,then Current date is Acceptable.

R5: if (1) Current month is in Apr-Nov &

(2) Current day of month is 15then Current date is Acceptable.15


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Facts

This space is a Parking Space. You live near this space. You have a Parking Permit.

Current month is in Apr-Nov. Current day is Tuesday. Current day of month is 15. Permit-Sign at this space.

You own a car. Your car is >5 years old. Current time is 3am. You have $18.00. ... 16


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Inference Graph

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You can park at this space

You have a Parking Permit This space is Permit-Parkable

Parking Space

Permit-Sign

Current date is Acceptable

15Apr-Nov

R1

R2

R5


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Additional Rules

R1: if(1) You have a Parking Permit & (2) This space is Permit-Parkable,


R2: if(1) This space is a Parking Space&

(2) Permit-Sign at this space &

(3) Current date is Acceptable,then This space is Permit-Parkable.

R3: if(1) Current time is 7am-Midnight&

(2) This space is Permit-Parkable,then You can park at this space.

R4: if (1) Current month is Dec-Mar,then Current date is Acceptable.

R5: if (1) Current month is in Apr-Nov&

(2) Current day of month is 15then Current date is Acceptable.

R7: if (1) You live near thisspace &

(2) You own a car & (3) You apply for a permit,

then You have a ParkingPermit.

R8: if (1) You can park at thisspacethen You can take a car.

18


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Inference Graph

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You can park at this space

You have a Parking Permit This space is Permit-Parkable

Parking Space

Permit-Sign

Current date is Acceptable

15Apr-Nov

You can take a car

live near

own a car

apply for permit

R7

R8

R1

R2

R5


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Mycin: What is the suspected portal of entry of ORGANISM-1 into this sterile site?

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Doctor: WHY

Mycin: [ie, why is it important to determine the site?]

[3.0] to determine which organism(s) to cover

It has already been established that

3.1] site of culture is blood

3.2] organism stain is gram positive

Therefore, if

3.3] portal of entry is g.i.

3.4] locus of infection is Pelvis or Abdomen,Then

strongly suggestive evidence (0.9) that therapy

should cover enterobacteriaceae.

[Rule 095]. . .


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Mycin: What is the suspected portal of entry of ORGANISM-1 into this sterile site?

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Doctor: WHY

Mycin: [ie, why is it important to determine the site?]

[3.0] to determine which organism(s) to cover

Ifhas already been established that

3.1] site of culture is blood

3.2] organism stain is gram positive

Therefore, if

3.3] portal of entry is g.i.

3.4] locus of infection is Pelvis or Abdomen,Then

strongly suggestive evidence (0.9) that therapy

should cover enterobacteriaceae.

[Rule 095]. . .


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Advantage of RuleTransparency

Explain reasoning

Support / Credability

Helpful when building/extending system

modifying system

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Issues

Faster Computation

User Interaction

Focus of Attention

Human Engineering

Variables

Control of Search Which (sub)goal? Which rule?

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Research Issues

Better Decision Making

Coping with Uncertainty

Better Explanation

Deeper Knowledge

First Principles

Meta

Acquiring the Knowledge

from expert

from data24

1.1 Expert System

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