36 - Logical

Prolog Topics Related to Assignment #8

The Facts

Data

• commission Mary Smith 300 19000 0.1

• commission Floyd Jenkins 500 3000 0.12

• commission Rose Harvey 500 20000 0.15

Predicates

• commission('Mary', 'Smith', 300, 19000, 0.1)

• commission('Floyd', 'Jenkins', 500, 3000, 0.12)

• commission('Rose', 'Harvey', 500, 20000, 0.15)

The Rules

pay(F, L, P) :- commission(F, L, Min, Sales, Crate),
    Sales * Crate > Min,
    P is Sales * Crate.

pay(F, L, P) :- commission(F, L, Min, Sales, Crate),
    Sales * Crate =< Min,
    P is Min.

Relational and Logical Operators

Numerical comparison operators:

• =:=

• =\=

• <

• =<

• >

• >=

String comparison operators:

• =

• \=

• @<

• @=<

• @>

• @>=

Logical operators:

• , is AND

• ; is OR

Selection

If A then B else C is written as

(A -> B ; C)

max(X, Y, Z) :-
    ( X =< Y -> Z = Y
    ; Z = X).

(Length > 0
    -> Avg is Sum / Length
    ; Avg is 0).

Multi-way selection:

(
    Op='eq', findall([X, Y, Z], (pay(X, Y, Z), Z=:=Ref), List);
    Op='ne', findall([X, Y, Z], (pay(X, Y, Z), Z=\=Ref), List);
    Op='gt', findall([X, Y, Z], (pay(X, Y, Z), Z>Ref), List);
    Op='ge', findall([X, Y, Z], (pay(X, Y, Z), Z>=Ref), List);
    Op='lt', findall([X, Y, Z], (pay(X, Y, Z), Z<Ref), List);
    Op='le', findall([X, Y, Z], (pay(X, Y, Z), Z=<Ref), List)
).

Rules for Queries

count(Op, Ref, Count) :- (
    Op=‘eq‘, findall(Z, (pay(X, Y, Z), Z=:=Ref), List),  length(List, Count);
    Op=‘ne‘, findall(Z, (pay(X, Y, Z), Z=\=Ref), List),  length(List, Count);
    Op=‘gt’, findall(Z, (pay(X, Y, Z), Z>Ref), List),  length(List, Count);
    Op=‘ge‘, findall(Z, (pay(X, Y, Z), Z>=Ref), List),  length(List, Count);
    Op=‘lt‘, findall(Z, (pay(X, Y, Z), Z<Ref), List),  length(List, Count);
    Op=‘le‘, findall(Z, (pay(X, Y, Z), Z=<Ref), List),  length(List, Count)
).

findAll

• findAll(Object, Goal, List).

• findAll([F, L], salaried(F, L, _), List). to find the name of all salaried employees

Six Queries

• list(Op, Ref, List).

• count(Op, Ref, List).

• min(Op, Ref, List).

• max(Op, Ref, List).

• total(Op, Ref, List).

• avg(Op, Ref, List).