Lecture 6 - Knowledge and Expert Systems

Question 1

Pre-1970s is known as the _________ Era

Answer 1

Heuristic Search Era

Question 2

In the Heuristic Search Era, the quest for the essence of intelligence focused on two areas:

Answer 2

Universal Problem Solving Techniques

Universal Learning Techniques

Question 3

Search techniques and General Problem Solving are both part of

Answer 3

Universal Problem Solving Techniques

Question 4

Perceptrons are part of

Answer 4

Universal Learning Techniques

Question 5

Both universal problem solving techniques and universal learning techniques are characterised by

Answer 5

Absence of a priori knowledge of the problem domain (i.e. no knowledge or understanding before the problem solving begins)

Question 6

Post 1970s is known as the

Answer 6

Knowledge Based Systems Era

Question 7

The Knowledge based systems era is characterised by

Answer 7

Recognition of central role of knowledge in all types of intelligent activity

Shift of research emphasis to study of techniques for representing and using knowledge

Question 8

What was Dendral?

Answer 8

The first serious attempt to produce a system as good as a human expert in a real world problem domain

Question 9

In what years was Dendral under devleopment?

Answer 9

1965-1972

Question 10

What was Dendral’s task?

Answer 10

Determine structure of a chemical compound from mass spectrogram data

Question 11

How does a mass spectrogram work?

Answer 11

Smash up molecules

Get a histogram of fragment masses

Question 12

What knowledge did dendral have?

Answer 12

Chemical formula of the compound

Atomic weights of chemicals and compounds

Question 13

Why was Dendral’s task particularly difficult?

Answer 13

Huge search space -

Atoms may be joined in many different configurations

Organic compound with only 20 atoms can have up to 10⁴ isomers

Question 14

What would be the naive solution to Dendral’s task, and why is it a stupid idea to use this?

Answer 14

Generate all possible structures of the compound

For each, check if it is consistent with spectral data

Not used because it is very computationally expensive

Question 15

What solution did dendral use for its task?

Answer 15

Use knowledge about the problem domain to constrain generation of candidate solutions

e.g. substructures the molecule is known to contain

substructures the molecule is known not to contain

which bonds are more likely to break

Far fewer candidates generated this way!

Question 16

What is the 8 Queens problem?

Answer 16

Illustration how the use of additional knowledge can reduce number of candidates in generate and test procedure:

place 8 queens on an 8x8 chessboard so no queen occupies a square attacked by any of the others

Question 17

What is the naive 8 queens solution?

Answer 17

Generate all possible configurations of 8 queens on a board

For each, check if it satisfies the conditions

Question 18

How many possible configurations of 8 queens are on a 8x8 chessboard?

Answer 18

64*63*62*61*60*59*58*57=2x10⁴

Checking a million configs a second would take 5.6 years to execute

Question 19

What constraint can be added to the 8 queens problem to reduce the number of configurations?

Answer 19

Only allow one queen in each row

no. solutions = 8⁸=2x10⁷

Execution time reduced to ~20 seconds

Question 20

What lessons can we learn from Dendral?

Answer 20

Searching is easy but time consuming

Intelligence lies in constraining the search to reduce time

Adding constraints is harder than programming a basic search

Constraints embody domain specific knowledge

Question 21

From Dendral we learn we need to replace this with

Answer 21

this

Question 22

What is a Production System?

Answer 22

A set of production rules

Question 23

What is a production rule?

Answer 23

Codify knowledge as a set of states and actions, e.g.

IF IT IS RAINING THEN PUT UP YOUR UMBRELLA

situation action

Question 24

Production rules are essentially

Answer 24

Ordered pairs

Question 25

The state component of a production rule is often called

Answer 25

condition

antecedent

left hand side or LHS

Question 26

The action component of a production rule is often called

Answer 26

Consequent

Right hand side or RHS

Question 27

What are the advantages of production systems?

Answer 27

Easy to program - if … then very basic construct

Modular - each bit of knowledge has its own rule - easy to add or remove rules

Easy to show user how the result was reached

Reaches decisions in a very natural fashion