Case-based Reasoning (CBR)• Collection of a set of cases

– Store a case in the Case Base• CBR is based on human information processing (HIP)

model in some problem areas– Thinking about how human processes information– Try to remember previous case/recall similar cases

& modify to fit a new situation• Examples: Law, diagnosis, strategic planning

– CEO: How should we modify last year’s plan?

• Human experts depend heavily on past experiences when solving new problems

Case-based Reasoning

• A CBR emulates this HIP model and maintains a historical case

• It retrieves cases relevant to the present problem situation from the case base and decides on the solution to the current problem on the basis of the outcomes from previous cases

CBR Components

• A case-based ES consists of– a case base– a retriever– an adapter– a refiner– an executer– an evaluator– (See diagram on next slide)

User Interface

Adapter

RefinerExecuter

Evaluator

Retriever

Case Base

Request RelevantPrior Cases

PriorResult

DraftSolution

RefinedSolution

New Cases(w/ Results)

SolutionPerformance

Casesw/o Results

CBR Components

Case-based Parts• A case base functions as a repository of

prior cases

• The cases are indexed ( a key as with a database) so that they can be quickly recalled when necessary

• A case contains the general descriptions of old problems

• In Knowledge Base: Set of Rules

• In Case Base: Set of Cases– Creates extra difficulty in retrieving

Case-base Parts - The Retriever

• When a new problem is entered into a case based system, a retriever decides on the features similar to the stored cases

• Retrieval is done by using features of the new cases as indexes into the case base

Case-based Parts - The Adapter

• An adapter examines the differences between these cases and the current problem

• It then applies rules to modify the old solution to fit the new problem

Case-based Parts - The Refiner

• A refiner critiques the adapted solution against prior outcomes

• One way to do this is to compare it to similar solutions of prior cases

• If a known failure exists for a derived solution, the system then decides whether the similarities is sufficient to suspect that the new solution will fail

Case-based Parts - The Executor

• Once a solution is critiqued, an executer applies the refined solution to the current problem

Case-based Parts - The Evaluator

• If the results are as expected, no further analysis is made, and the cases and its solution is stored for use in future problem solving

• If not, the solution is repaired

Model-based Reasoning• A model-based system is based on a model of the

structure and behavior of the device that the system is designed to simulate

• Used for well structured problems– Not for stock pricing/modeling, not well

structured– Engineering Problems

• Ex: Diagnosing hardware or a machine• Ex: Automobile diagnostics

• Based on written documentation• The problem is extracting knowledge

Model-based Reasoning

• Observed behavior (what the device is actually doing) is compared with predicted behavior (what the device should do)

• The difference between them is called a discrepancy, indicating a defect

• Then a process is initiated to diagnose the nature and location of the defect

• Could be a mathematical equation

ActualDevice Model

PredictedBehavior

ObservedBehavior

Discrepancy

Model-based Reasoning

Model-based Reasoning• Correct Operation:• Assume we have a model-based system built to diagnose the

following simple device with 3 multipliers and 2 adders• Once the logic is developed, executes quickly

A = 3

B = 3

C = 2

D = 2

A = 3

Mult - 1

Mult - 2

Mult -3

Add - 3

Add - 3

F = 12

G = 12

3

2

3

2

2

3

6

6

6

6

6

6

6

12

12

Model-based Reasoning• Incorrect Operation:

– Diagnostics

A = 3

B = 3

C = 2

D = 2

A = 3

Mult - 1

Mult - 2

Mult -3

Add - 3

Add - 3

F = 10

G = 12

3

2

3

2

2

3

6

6

6

6

6

6

6

10

12

6

6

6

Culprit of problem?No - 6 comes out

Culprit of problem?No - 6 comes out

Culprit of problem?No - 6 comes out

Culprit of problem?Yes - 10 comes out,

problem with Carry Bit

Predicate Logiccan be used here