Forward and Backward Chaining Example

1. RULED-BASED EXPERT SYSTEM
(FORWARD CHAINING AND BACKWARD CHAINING)
-Amit Singh Dahal
-g5638545

2. FIRST STEP: WRITE THE RULES BASED ON
DIAGRAMS:
 R1: IF the animal has hair
THEN it is a mammal
 R2: IF the animal gives milk
THEN it is a mammal
 R3: IF the animal has feathers
THEN it is a bird
 R4: IF the animal flies
the animal lays eggs
THEN it is a bird
 R5: IF the animal is a mammal
the animal eats meat
THEN it is a carnivore

3. CONTD…
 R6: IF the animal is a mammal
the animal has pointed teeth
the animal has claws
the animal's eyes point forward
THEN it is a carnivore
 R7: IF the animal is a mammal
the animal has hooves
THEN it is an ungulate
 R8: IF the animal is a mammal
the animal chews cud
THEN it is an ungulate AND
it is even-toed

4. CONTD…
 R9: IF the animal is a carnivore
the animal has a tawny colour
the animal has dark spots
THEN it is a cheetah
 R10: IF the animal is a carnivore
the animal has a tawny colour
the animal has black stripes
THEN it is a tiger
 R11: IF the animal is an ungulate
the animal has long legs
the animal has a long neck
the animal has dark spot
THEN it is a giraffe
 R12: IF the animal is an ungulate
the animal has a white colour
the animal has black stripes
THEN it is a zebra

5. CONTD…
 R13 :IF the animal is a bird
the animal does not fly
the animal has long legs
the animal has a long neck
the animal is black and white
THEN it is an ostrich
 R14 :IF the animal is a bird
the animal does not fly
the animal swims
the animal is black and white
THEN it is a penguin
 R15 :IF the animal is a bird
the animal is a good flier
THEN it is an albatross

6. FORWARD CHAINING
 Facts in the working memory:
-the animal gives milk
-the animal chew cuds
-the animal has long legs
-the animal has a long neck
-the animal has a dark spot
 Assume GOAL:
the animal is Giraffe

7.  Round 1:
R2: IF the animal gives milk
THEN it is a mammal  fires mammal
 Round 2:
R8: IF the animal is mammal
the animal chews cud
THEN it is an ungulate  fires ungulate
 Round 3:
R11: IF the animal is an ungulate
the animal has long legs
the animal has a long neck
the animal has dark spot
THEN it is a GIRAFFE
Hence, goal reached. The used rules are: R2, R8
and R11.

8. BACKWARD CHAINING
 Facts in the working memory:
-the animal has hair
-the animal has claws
-the animal has pointed teeth
-the animal’s eyes point forward
-the animal has a tawny color
-the animal has dark spots
 Assume GOAL:
the animal is Cheetah

9.  Pass 1:
Based on R9:
?the animal is carnivore
the animal has a tawny color
the animal has dark spot
Stack:
Cheetah
S1
S1
AND

10.  Pass 2:
Based on R5 and R6:
?the animal is a mammal
?the animal can eat meat
?the animal is a mammal
the animal has pointed teeth
the animal has claws
the animal eyes point forward
Stack:
AND
AND
OR
S2
Carnivore
S1
S2

11.  Pass 3:
Based on R1 and R2:
the animal has hair
the animal gives milk
Stack:
OR Mammal
S1
S2

12.  Pass 4:
Based on R5 and R6:
 the animal is a mammal
? the animal can eat meat
 the animal is a mammal
the animal has pointed teeth
the animal has claws
the animal eyes point forward
Stack:
AND
OR
AND
Carnivore
S1

13.  Pass 5:
 the animal is carnivore
the animal has a tawny color
the animal has dark spot
Stack: Clear
Hence, goal is correct using backward chaining
provided the information and the rules used are:
R9, R6, R1.
AND Cheetah

14. THE END
Any Questions??