Exercise 5.13 In this question, consider using integrity constraints and consistency-based diagnosis in a purchasing agent that interacts with various information sources on the web. To answer a question, the purchasing agent will ask a number of the information sources for facts. However, information sources are sometimes wrong. It is useful to be able to automatically determine which information sources may be wrong when a user gets conflicting information.

In this question we consider how integrity constraints and assumables can be used to determine what errors are present in different information sources.

In this question, we use meaningless symbols such as

a, b,

c, . . ., but in a real domain there will be meaning associated with the symbols, such as a meaning

“there is skiing in Hawaii” and z meaning “there is no skiing in Hawaii”, or a meaning “butterflies do not eat anything” and z meaning “butterflies eat nectar”.

We will use meaningless symbols in this question because the computer does not have access to the meanings and must simply treat them as meaningless symbols.

Suppose the following information sources and associated information are provided:

Source s1: Source s1 claims the following clauses are true:

a ← h.

d ← c.

Source s2: Source s2 claims the following clauses are true:

e ← d.

f ← k.

z ← g.

j.