This document provides examples of forward chaining and backward chaining for a knowledge base about animals. The forward chaining example starts with the fact that Fritz croaks and eats flies, and uses rules in the knowledge base to infer that Fritz is a frog and is colored green. The backward chaining example starts with the goal of determining Fritz's color, and works backwards from rules in the knowledge base to reach the same conclusion.

1. Forward & backward
chaining
By
Md. Fazle Rabbi
16CSE057

2. 4.2
Forward chaining

3. 4.3
• Forward chaining: We start with the sentences in the
knowledge base and generate new conclusions that in
turn can allow more inferences to be made.
• data-driven
• Automatic, unconscious processing
• May do lots of work that is irrelevant to the goal
Forward chaining

4. 4.4
• It is a down-up approach, as it moves from bottom to top.
• It is a process of making a conclusion based on known facts or
data, by starting from the initial state and reaches the goal
state.
• Forward-chaining approach is also called as data-driven as we
reach to the goal using available data.
• Forward -chaining approach is commonly used in the expert
system, such as CLIPS, business, and production rule systems.
Properties of Forward-Chaining

5. 4.5
Forward Chaining Example
• Knowledge Base:
• If [X croaks and eats flies] Then [X is a frog]
• If [X chirps and sings] Then [X is a canary]
• If [X is a frog] Then [X is colored green]
• If [X is a canary] Then [X is colored yellow]
• [Fritz croaks and eats flies]
• Goal:
• [Fritz is colored Y]?

6. 4.6
Forward Chaining Example
Knowledge Base
If [X croaks and eats flies]
Then [X is a frog]
If [X chirps and sings]
Then [X is a canary]
If [X is a frog]
Then [X is colored green]
If [X is a canary]
Then [X is colored yellow]
[Fritz croaks and eats flies]
Goal
[Fritz is colored Y]?

7. 4.7
Forward Chaining Example
Knowledge Base
If [X croaks and eats flies]
Then [X is a frog]
If [X chirps and sings]
Then [X is a canary]
If [X is a frog]
Then [X is colored green]
If [X is a canary]
Then [X is colored yellow]
[Fritz croaks and eats flies]
Goal
[Fritz is colored Y]?

8. 4.8
Forward Chaining Example
Knowledge Base
If [X croaks and eats flies]
Then [X is a frog]
If [X chirps and sings]
Then [X is a canary]
If [X is a frog]
Then [X is colored green]
If [X is a canary]
Then [X is colored yellow]
[Fritz croaks and eats flies]
Goal
[Fritz is colored Y]?
If [X croaks and eats flies]
Then [X is a frog]
[Fritz croaks and eats flies]
[Fritz is a frog]

9. 4.9
Forward Chaining Example
If [X croaks and eats flies]
Then [X is a frog]
[Fritz croaks and eats flies]
[Fritz is a frog]
Knowledge Base
If [X croaks and eats flies]
Then [X is a frog]
If [X chirps and sings]
Then [X is a canary]
If [X is a frog]
Then [X is colored green]
If [X is a canary]
Then [X is colored yellow]
[Fritz croaks and eats flies]
[Fritz is a frog]
Goal
[Fritz is colored Y]?

10. 4.10
Forward Chaining Example
If [X croaks and eats flies]
Then [X is a frog]
[Fritz croaks and eats flies]
[Fritz is a frog]
Knowledge Base
If [X croaks and eats flies]
Then [X is a frog]
If [X chirps and sings]
Then [X is a canary]
If [X is a frog]
Then [X is colored green]
If [X is a canary]
Then [X is colored yellow]
[Fritz croaks and eats flies]
[Fritz is a frog]
Goal
[Fritz is colored Y]?
?

11. 4.11
Forward Chaining Example
If [X croaks and eats flies]
Then [X is a frog]
[Fritz croaks and eats flies]
[Fritz is a frog]
Knowledge Base
If [X croaks and eats flies]
Then [X is a frog]
If [X chirps and sings]
Then [X is a canary]
If [X is a frog]
Then [X is colored green]
If [X is a canary]
Then [X is colored yellow]
[Fritz croaks and eats flies]
[Fritz is a frog]
Goal
[Fritz is colored Y]?

12. 4.12
Forward Chaining Example
If [X croaks and eats flies]
Then [X is a frog]
[Fritz croaks and eats flies]
[Fritz is a frog]
Knowledge Base
If [X croaks and eats flies]
Then [X is a frog]
If [X chirps and sings]
Then [X is a canary]
If [X is a frog]
Then [X is colored green]
If [X is a canary]
Then [X is colored yellow]
[Fritz croaks and eats flies]
[Fritz is a frog]
Goal
[Fritz is colored Y]?
If [X is a frog]
Then [X is colored green]
[Fritz is colored green]

13. 4.13
Forward Chaining Example
If [X croaks and eats flies]
Then [X is a frog]
[Fritz croaks and eats flies]
[Fritz is a frog]
If [X is a frog]
Then [X is colored green]
[Fritz is colored green]
Knowledge Base
If [X croaks and eats flies]
Then [X is a frog]
If [X chirps and sings]
Then [X is a canary]
If [X is a frog]
Then [X is colored green]
If [X is a canary]
Then [X is colored yellow]
[Fritz croaks and eats flies]
[Fritz is a frog]
[Fritz is colored green]
Goal
[Fritz is colored Y]?

14. 4.14
Forward Chaining Example
If [X croaks and eats flies]
Then [X is a frog]
[Fritz croaks and eats flies]
[Fritz is a frog]
If [X is a frog]
Then [X is colored green]
[Fritz is colored green]
Knowledge Base
If [X croaks and eats flies]
Then [X is a frog]
If [X chirps and sings]
Then [X is a canary]
If [X is a frog]
Then [X is colored green]
If [X is a canary]
Then [X is colored yellow]
[Fritz croaks and eats flies]
[Fritz is a frog]
[Fritz is colored green]
Goal
[Fritz is colored Y]?
?

15. 4.15
Forward Chaining Example
If [X croaks and eats flies]
Then [X is a frog]
[Fritz croaks and eats flies]
[Fritz is a frog]
If [X is a frog]
Then [X is colored green]
[Fritz is colored green]
Knowledge Base
If [X croaks and eats flies]
Then [X is a frog]
If [X chirps and sings]
Then [X is a canary]
If [X is a frog]
Then [X is colored green]
If [X is a canary]
Then [X is colored yellow]
[Fritz croaks and eats flies]
[Fritz is a frog]
[Fritz is colored green]
Goal
[Fritz is colored Y]?

16. 4.16
Forward Chaining Example
If [X croaks and eats flies]
Then [X is a frog]
[Fritz croaks and eats flies]
[Fritz is a frog]
If [X is a frog]
Then [X is colored green]
[Fritz is colored green]
Knowledge Base
If [X croaks and eats flies]
Then [X is a frog]
If [X chirps and sings]
Then [X is a canary]
If [X is a frog]
Then [X is colored green]
If [X is a canary]
Then [X is colored yellow]
[Fritz croaks and eats flies]
[Fritz is a frog]
[Fritz is colored green]
Goal
[Fritz is colored Y]?
[Fritz is colored Y] ?
Y = green

17. 4.17
Backward chaining

18. 4.18
• Backward chaining: We start with something we want
to prove, find implication sentences that would allow
us to conclude it, and then attempt to establish their
premises in turn.
• goal-driven
• Where are my keys? How do I get to my next class
Backward chaining

19. 4.19
Properties of backward chaining
• It is known as a top-down approach.
• In backward chaining, the goal is broken into
sub-goal or sub-goals to prove the facts true.
• It is called a goal-driven approach, as a list of
goals decides which rules are selected and used.
• The backward-chaining method mostly used a
depth-first search strategy for proof.

20. 4.20
Backward Chaining Example
Knowledge Base
If [X croaks and eats flies]
Then [X is a frog]
If [X chirps and sings]
Then [X is a canary]
If [X is a frog]
Then [X is colored green]
If [X is a canary]
Then [X is colored yellow]
[Fritz croaks and eats flies]
Goals
[Fritz is colored Y]?

21. 4.21
Backward Chaining Example
Knowledge Base
If [X croaks and eats flies]
Then [X is a frog]
If [X chirps and sings]
Then [X is a canary]
If [X is a frog]
Then [X is colored green]
If [X is a canary]
Then [X is colored yellow]
[Fritz croaks and eats flies]
Goals
[Fritz is colored Y]?

22. 4.22
Backward Chaining Example
Knowledge Base
If [X croaks and eats flies]
Then [X is a frog]
If [X chirps and sings]
Then [X is a canary]
If [X is a frog]
Then [X is colored green]
If [X is a canary]
Then [X is colored yellow]
[Fritz croaks and eats flies]
Goals
[Fritz is colored Y]?
[Fritz is colored Y]
If [X is a frog]
Then [X is colored green]
[X is a frog]

23. 4.23
Backward Chaining Example
[Fritz is colored Y]
If [X is a frog]
Then [X is colored green]
[X is a frog]
Knowledge Base
If [X croaks and eats flies]
Then [X is a frog]
If [X chirps and sings]
Then [X is a canary]
If [X is a frog]
Then [X is colored green]
If [X is a canary]
Then [X is colored yellow]
[Fritz croaks and eats flies]
Goals
[Fritz is colored Y]?
[X is a frog]

24. 4.24
Backward Chaining Example
[Fritz is colored Y]
If [X is a frog]
Then [X is colored green]
[X is a frog]
Knowledge Base
If [X croaks and eats flies]
Then [X is a frog]
If [X chirps and sings]
Then [X is a canary]
If [X is a frog]
Then [X is colored green]
If [X is a canary]
Then [X is colored yellow]
[Fritz croaks and eats flies]
Goals
[Fritz is colored Y]?
[X is a frog]

25. 4.25
Backward Chaining Example
[Fritz is colored Y]
If [X is a frog]
Then [X is colored green]
[X is a frog]
Knowledge Base
If [X croaks and eats flies]
Then [X is a frog]
If [X chirps and sings]
Then [X is a canary]
If [X is a frog]
Then [X is colored green]
If [X is a canary]
Then [X is colored yellow]
[Fritz croaks and eats flies]
Goals
[Fritz is colored Y]?
[X is a frog]
If [X is a canary]
Then [X is colored yellow]
[X is a canary]

26. 4.26
Backward Chaining Example
[Fritz is colored Y]
If [X is a frog]
Then [X is colored green]
[X is a frog]
If [X is a canary]
Then [X is colored yellow]
[X is a canary]
Knowledge Base
If [X croaks and eats flies]
Then [X is a frog]
If [X chirps and sings]
Then [X is a canary]
If [X is a frog]
Then [X is colored green]
If [X is a canary]
Then [X is colored yellow]
[Fritz croaks and eats flies]
Goals
[Fritz is colored Y]?
[X is a frog]
[X is a canary]

27. 4.27
Backward Chaining Example
[Fritz is colored Y]
If [X is a frog]
Then [X is colored green]
[X is a frog]
If [X is a canary]
Then [X is colored yellow]
[X is a canary]
Knowledge Base
If [X croaks and eats flies]
Then [X is a frog]
If [X chirps and sings]
Then [X is a canary]
If [X is a frog]
Then [X is colored green]
If [X is a canary]
Then [X is colored yellow]
[Fritz croaks and eats flies]
Goals
[Fritz is colored Y]?
[X is a frog]
[X is a canary]

28. 4.28
Backward Chaining Example
[Fritz is colored Y]
If [X is a frog]
Then [X is colored green]
[X is a frog]
If [X is a canary]
Then [X is colored yellow]
[X is a canary]
Knowledge Base
If [X croaks and eats flies]
Then [X is a frog]
If [X chirps and sings]
Then [X is a canary]
If [X is a frog]
Then [X is colored green]
If [X is a canary]
Then [X is colored yellow]
[Fritz croaks and eats flies]
Goals
[Fritz is colored Y]?
[X is a frog]
[X is a canary]
If [X croaks and eats flies]
Then [X is a frog]
[X croaks and eats flies]

29. 4.29
Backward Chaining Example
[Fritz is colored Y]
If [X is a frog]
Then [X is colored green]
[X is a frog]
If [X is a canary]
Then [X is colored yellow]
[X is a canary]
If [X croaks and eats flies]
Then [X is a frog]
[X croaks and eats flies]
Knowledge Base
If [X croaks and eats flies]
Then [X is a frog]
If [X chirps and sings]
Then [X is a canary]
If [X is a frog]
Then [X is colored green]
If [X is a canary]
Then [X is colored yellow]
[Fritz croaks and eats flies]
Goals
[Fritz is colored Y]?
[X is a frog]
[X is a canary]
[X croaks and eats flies]

30. 4.30
Backward Chaining Example
[Fritz is colored Y]
If [X is a frog]
Then [X is colored green]
[X is a frog]
If [X is a canary]
Then [X is colored yellow]
[X is a canary]
If [X croaks and eats flies]
Then [X is a frog]
[X croaks and eats flies]
Knowledge Base
If [X croaks and eats flies]
Then [X is a frog]
If [X chirps and sings]
Then [X is a canary]
If [X is a frog]
Then [X is colored green]
If [X is a canary]
Then [X is colored yellow]
[Fritz croaks and eats flies]
Goals
[Fritz is colored Y]?
[X is a frog]
[X is a canary]
[X croaks and eats flies]

31. 4.31
Backward Chaining Example
[Fritz is colored Y]
If [X is a frog]
Then [X is colored green]
[X is a frog]
If [X is a canary]
Then [X is colored yellow]
[X is a canary]
If [X croaks and eats flies]
Then [X is a frog]
[X croaks and eats flies]
Knowledge Base
If [X croaks and eats flies]
Then [X is a frog]
If [X chirps and sings]
Then [X is a canary]
If [X is a frog]
Then [X is colored green]
If [X is a canary]
Then [X is colored yellow]
[Fritz croaks and eats flies]
Goals
[Fritz is colored Y]?
[X is a frog]
[X is a canary]
[X croaks and eats flies]
[Fritz croaks and eats flies]
X = Fritz, Y = green

32. 4.32
Thank you