← IGCSE Computer Science Paper 1

The four parts of an expert system

The four parts of an expert system: the knowledge base holds facts, the rule base holds rules, the inference engine reasons, and the interface talks to the user.

Part of: IGCSE Computer Science 0478 — 6.3 Artificial Intelligence — Module 11

Understanding The four parts of an expert system in IGCSE Computer Science Paper 1

What it does: A rule base is made of rules written in an IF ... THEN form, which the inference engine uses to reach conclusions. The interface is the part that talks to the user. It asks questions, takes the inputs and shows the output, so a prompt like this belongs to the interface. The knowledge base is the store of facts about the topic, such as symptoms and diseases in a medical expert system. Students often confuse the interface with the inference engine. The interface communicates with the user, while the inference engine does the reasoning.

Common mistakes: The knowledge base holds facts. The rules are held in the rule base, so line 2 should say 'holds facts'. The inference engine does the reasoning by applying the rules to the facts. Facts are held in the knowledge base, so it should say 'reasons'.

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Learning
Duo
Which list names all four parts of an expert system?
Knowledge base, rule base, inference engine, interfaceKnowledge base, rule base, processor, monitor
Matches
The rule base stores all the facts about the subject, such as a list of diseases.
↓
Facts are stored in the knowledge base, not the rule base. The rule base only stores the IF-THEN rules.
Applying
Meanings
Term
knowledge base, rule base, inference engine, interface
Meaning
The four parts of an expert system: the knowledge base holds facts, the rule base holds rules, the inference engine reasons, and the interface talks to the user.
Practice
EXPERT SYSTEM
Testing
Gaps
The holds the facts
Check Answer
Spots
1parts of an expert system
2knowledge base: holds rules

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Quick Questions

1. Which list names all four parts of an expert system?
A. Knowledge base, rule base, processor, monitor
B. Knowledge base, rule base, inference engine, interface ✓
An expert system has exactly four parts: the knowledge base, the rule base, the inference engine and the interface.
2. Which part of an expert system holds the facts about the subject?
A. Knowledge base ✓
B. Rule base
The knowledge base stores the facts. The rule base stores the IF-THEN rules used to reason about those facts.
3. Which part holds the IF-THEN rules?
A. Rule base ✓
B. Interface
The rule base is the collection of rules. The interface is only how the user talks to the system.
4. Which part does the reasoning, matching the user's answers to the rules and facts to reach a conclusion?
A. Inference engine ✓
B. Knowledge base
The inference engine does the reasoning. The knowledge base only stores facts and does not reason.
5. A doctor types symptoms into a screen and reads the advice that appears. Which part is the doctor using?
A. Inference engine
B. Interface ✓
The interface lets the user enter questions and see the results. The inference engine works behind the scenes.

Match the Pairs

knowledge base → The part of an expert system that stores the facts and data about the subject area, gathered from human experts.
inference engine → The part of an expert system that reasons: it searches the knowledge base and applies the rules to reach a conclusion.
The rule base holds IF-THEN rules that link facts to conclusions. → IF fever = TRUE AND rash = TRUE THEN suggest measles
The interface is how the user enters answers and sees the conclusion. → OUTPUT "Do you have a fever? (Y/N)"
The rule base stores all the facts about the subject, such as a list of diseases. → Facts are stored in the knowledge base, not the rule base. The rule base only stores the IF-THEN rules.
The interface decides the conclusion by applying the rules to the facts. → Reasoning is done by the inference engine. The interface only handles input from the user and output to the user.

Key Term

knowledge base, rule base, inference engine, interface
The four parts of an expert system: the knowledge base holds facts, the rule base holds rules, the inference engine reasons, and the interface talks to the user.

Fill in the Blanks

1. The knowledge base holds the facts
Hint: Type the name of the part that stores the facts about the topic
2. The rule base stores the IF-THEN rules
Hint: Type the name of the part that stores the rules
3. The inference engine applies rules to facts
Hint: Type the name of the part that does the reasoning to reach a conclusion
4. The interface lets the user ask questions
Hint: Type the name of the part the user types questions into and reads answers from
5. User <-> interface <-> inference engine <-> knowledge base + rule base
Hint: Type the part that sits between the interface and the stored facts and rules

Spot the Error

Question 1
A parts of an expert system
B knowledge base: holds rules
C rule base: holds IF-THEN rules
D inference engine: reasons
Line B — The knowledge base holds facts. The rules are held in the rule base, so line 2 should say 'holds facts'.
Question 2
A inference engine: holds facts
B interface: talks to the user
C knowledge base: holds facts
D rule base: holds rules
Line A — The inference engine does the reasoning by applying the rules to the facts. Facts are held in the knowledge base, so it should say 'reasons'.
Question 3
A USER <-> rule base
B interface <-> inference engine
C engine <-> knowledge base
D engine <-> rule base
Line A — The user only communicates with the interface, never directly with the rule base. Line 1 should be USER <-> interface.
Question 4
A kb = list of facts
B rb = the user screen
C ie = reasons using kb and rb
D ui = talks to the user
Line B — The rule base (rb) holds the IF-THEN rules. The user screen is the interface, so line 2 should be rb = list of IF-THEN rules.
Question 5
A Car fault expert system
B knowledge base: engine facts
C rule base: IF-THEN fault rules
D inference engine: asks user
E interface: asks the user
Line D — Asking the user questions is the job of the interface. The inference engine reasons using the facts and rules, so line 4 should say 'reasons'.

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