Question

Consider the following system of rules and facts, where the variable x stands for a patient, “red_spots(x)” stands for “patient x has red spots”, and so forth.

Rules:

• R1: if fever(x) AND red_spot(x), then measles(x)
• R2: if running_nose(x), then cold(x)
• R3: if cold(x), then contagious(x)
• R4: if fever(x) AND stiff_neck(x), then meningitis(x)
• R5: if measles(x), then contagious(x)
• R6: if meningitis(x), then contagious(x)
• R7: if contagious(x) and dangerous(x), then isolated(x)
• R8: if meningitis(x), then dangerous(x)

Initial facts: running_nose(mary), red_spots(mary), stiff_neck(john), fever(mary), fever(john)

a) What can be derived from this knowledge base by Forward chaining? Please show your work step by step;

b) How can isolated(john) be derived by Backward chaining? Show your work step by step.

Answer 1

Answer (A) Below is derived from this knowledge base by Forward chaining
​​​​​​In forward chaining we use all the rules started from already stated facts to reach to conclusion(goal).
This is bottom-up approach.

Answer (B) Below if isolated(john) derived by Backward chaining.

Here we move backwards from solution to determine initial rules and conditions. This only test for certain given and selected rules. Backward chaining uses top-down approach.