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
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
