Expert System: Rule Based

Question 1

What is a conflict set of rules in a rule-based expert system?

Answer 1

• The inference engine compares IF (condition) parts of the rules with data available in the database, and when conditions are satisfied the rules are set to fire.
• The firing of one rule may affect the activation of other rules, and therefore the inference engine must allow only one rule to fire at a time.
• two rules with the same IF part.
• Thus both of them can be set to fire when the condition part is satisfied.
• These rules represent a conflict set.
• The inference engine must determine which rule to fire from such a set

Rule 1:
IF the ‘traffic light’ is green THEN the action is go

Rule 2:
IF the ‘traffic light’ is red THEN the action is stop

Rule 3:
IF the ‘traffic light’ is red THEN the action is go

Question 2

Define conflict resultion.

Answer 2

A method for choosing a rule to fire when more than one rule can be fired in a given cycle is called conflict resolution.

Question 3

How can we resolve a conflict in obvious way?

Answer 3

• The obvious strategy for resolving conflicts is to
  
  • establish a goal and
  • stop the rule execution when the goal is reached.

In our problem, for example, the goal is to establish a value for linguistic object action. When the expert system determines a value for action, it has reached the goal and stops. Thus if the traffic light is red, Rule 2 is executed, object action attains value stop and the expert system stops. In the given example, the expert system makes a right decision; however if we arranged the rules in the reverse order, the conclusion would be wrong. It means that the rule order in the knowledge base is still very important.

Question 4

Name alternative Conflict Resolution Strategies.

Answer 4

• Fire the rule with the highest priority.
  
  • In simple applications, the priority can be established by placing the rules in an appropriate order in the knowledge base.
• Fire the most specific rule.
  
  • This method is also known as the longest matching strategy. It is based on the assumption that a specific rule processes more information than a general one
• Fire the rule that uses the data most recently entered in the database.
  
  • This method relies on time tags attached to each fact in the database.

Question 5

What is an Inference Engine

Answer 5

takes rules, takes facts

IF THEN – rule

A == fact

arrives at conclusiion by combingin them

Question 6

What isForward Chaining?

Answer 6

• data driven approach
• reasoning starts with data
• data is matched with rule
• each cycle only top most rule is executed
• a new fact is derrived
• macht-fire cycle stops when there are no more rules

Question 7

Why can backward chaining be more efficient?

Answer 7

• many rules can be fire that hav nothitng to do with our goal
• inefficient
• if we only want to infer a particular fact, backback chaining may be the way to go