Lecture 7 - Forward Chaining

Question 1

What does a production rule interpreter do?

Answer 1

Interprets or uses the rules in a production system

Question 2

What are the two most common types of production rule interpreters?

Answer 2

Forward Chainers and Backward Chainers

Question 3

Production rule interpreters ________ access the rules in a production system

Answer 3

systematically

Question 4

What are the core components of a production system?

Answer 4

Set of production rules - aka rule base

Interpreter - selects and applies rules

Environment - entities that the actions and conditions relate to

Question 5

What are the components of the environment of a production system?

Answer 5

Dynamic - information that determines which rules fire, modified by the rules - aka working memory

Static - information used to match conditions and determine actions

Question 6

What are the two steps a forward chaining rule interpreter goes through? (and what is involved in the step)

Answer 6

Match step - scan through the rules to find one whose condition matches the current state

Execute/Firing step - Perform the action of the matched rule

Question 7

Which step of the match-execute cycle is likely to change the environment of a production system?

Answer 7

Execute step

Question 8

Until when does the match-execute cycle of an interpreter continue?

Answer 8

no rule matches

or

system is stopped by the action of a rule

Question 9

When a rule is interpreted and executed, the system

a) may

or b) may not

ask the user for input

Answer 9

may

Question 10

In forward chaining systems, the property called refractoriness means what?

Answer 10

The same rule is not allowed to fire twice from matching the same facts (prevents infinite loops)

Question 11

Conflict Resolution Strategies are needed when

Answer 11

Two or more rules match at the same time

Question 12

What are 5 conflict resolution strategies?

Answer 12

First Match Found

Random Choice

Specificity

Recency

Assigned Priorities

Question 13

Describe the first match found conflict resolution strategy

Answer 13

First matching rule is executed regardless of any other matching rules

Rarely used now

Question 14

Describe the random choice conflict resolution strategy

Answer 14

Randomly selects a rule to execute from matching rules

Makes behaviour non-deterministic, rarely used

Question 15

Describe the Specificity conflict resolution strategy

Answer 15

Choose the rule which has the most restrictive condition part

Easy to handle exceptional cases

Widely used

Question 16

Describe the recency conflict resolution strategy

Answer 16

Choose the rule whose condition was most recently matched

Tends to keep system focused on same part of problem until it has been resolved

Widely used

Question 17

Describe the assigned priorities conflict resolution strategy

Answer 17

Programmer assigns each rule a numerical priority. Highest priority rule is chosen

Question 18

What are 3 features of forward chaining

Answer 18

Data driven - no explicit goal, behaviour is determined by current situation

Rule selection - Rules chosen are those whose conditions match the current situation

Iterative - repeated execution of the match-execute cycle