Suppose we put into a logical database a segment of the U.S. census data listing the age, city of residence, date of birth, and mother of every person, using social security numbers as identifying constants for each person. Thus, George’s age is given by Age (443-65-1282, 56). Which of the indexing schemes S1 —S5 following enable an efficient solution for which of the queries Q1—Q4 (assuming normal backward chaining)?

S1: an index for each atom in each position.

S2; an index for each first argument

S3: an index for each predicate atom.

S4: an index for each combination of predicate and first argument.

S5: an index for each combination of predicate and second argument and an index for each first argument (nonstandard).

Q1: Age (443-44-4321, x)

Q2: Resides In (x. Houston)

Q3: Mother (x, y)

Q4: Age (x, 34) ^ Resides In (x, Tiny Town USA)