CSCI 3137 - Logic Programming with Prolog

Questions and Answers

What happens when two free variables A and B are unified?

They refer to the same object. (correct)

They become bound to specific objects.

They no longer exist.

They can reference different objects.

Which of the following pairings is not valid for unification in compound terms?

f(a) = f(a)

f(A) = f(a)

f(a) = f(a, b) (correct)

f(a) = g(a) (correct)

Why can't the variable A in f(A, b) = f(a, A) be unified with both a and b?

Variables cannot be unified at all.

It can only be bound to one term at a time. (correct)

A is a compound term.

Both a and b are atoms.

What is the correct structure of a rule in Prolog?

head :- term_1, term_2,..., term_n. Signup and view all the answers

Which of the following statements best describes facts in Prolog?

They express non-conditional statements that are true. Signup and view all the answers

In the expression parent(GP, GC) :- parent(GP, P), parent(P, GC), what does GP represent?

A free variable. Signup and view all the answers

What will the unification f(a) = f(b) return?

It will indicate a failure of unification. Signup and view all the answers

If two compound terms have different names, what is the result of attempting to unify them?

The unification will fail. Signup and view all the answers

Which statement about compound term unification is false?

Names of the terms can be different. Signup and view all the answers

In the context of Prolog, what is the main purpose of rules?

To derive new facts from existing ones. Signup and view all the answers

Study Notes

SWI-Prolog Overview

SWI-Prolog is a free implementation of the Prolog programming language, developed at the University of Amsterdam.
Available for download at http://swi-prolog.org, with a web-based version, SWISH, accessible at http://swish.swi-prolog.org.
Prolog files use the .pl extension.

Prolog Program Structure

Programs consist of facts, predicates, relations defined as true, and rules that establish relationships between predicates.
Distinction exists between functional programming (using functions) and logical programming (using predicates).

Querying in Prolog

Prolog uses a querying system instead of traditional execution.
Queries determine if a statement can be proven from existing facts and rules.
The predicate plus(Addend1, Addend2, Sum) checks if Addend1 + Addend2 = Sum.
Examples of queries:
- ?- plus(1, 2, 3). asks if 1 + 2 equals 3.
- ?- plus(1, 2, Sum). seeks the value of Sum that satisfies the equation.

Atoms in Prolog

Atoms serve as tokens with meaning defined by the programmer (e.g., socrates could represent a person or a pet).
Example: GP is a grandparent of GC if there exists a parent-child relationship.

Query Resolution Mechanism

Prolog resolves queries by unifying them with facts or rules.
A successful unification with a fact indicates truth; with a rule, the rule's body becomes the subgoal.
Multiple potential unifying facts/rules create choice points in Prolog.

Handling Query Failure

A query failure signifies that a statement cannot be proven, not necessarily that it is false.

Conjunction in Prolog

Expressions can be evaluated for equality or inequality using =:= and =\= respectively.
Example rules show how comparisons between expressions are made.

Arithmetic Operations

Term1 = Term2 denotes unification, while Expr1 =:= Expr2 represents mathematical equality.
Example: 1 =:= 1.0 is true, but 1 = 1.0 is false due to type differences.

Lists in Prolog

Lists are structured as a head element(s) followed by a tail list, similar to structures in Scheme.

Variable Unification

Unifying two free variables creates a single variable with multiple designations.
Example: A = B links both names to the same unidentified object.

Unification of Compound Terms

Compound terms unify only if they share the same name and arity, with corresponding arguments also unifying.
Examples:
- f(a) = f(a) is valid.
- f(a) = g(a) fails due to differing names.

Rules and Facts in Prolog

Facts convey unconditional truths and are declared with syntax ending in a period, e.g., parent(marge, maggie).
Rules derive new facts from known ones, formatted as head :- term_1, term_2,..., term_n.
Example: grandparent(GP, GC) :- parent(GP, P), parent(P, GC). demonstrates how to establish grandparent relationships through parenthood.

Description

This quiz covers the fundamental principles of logic programming using SWI-Prolog, including installation and usage details. Explore the features of this powerful programming language and understand its application in various programming contexts.