Prolog

Question 1

The aim of prolog is to

Answer 1

• represent knowledge efficiently through facts and rules
• retrieve and infer knowledge from this representation,
  given a query

Question 2

Logical principles are needed to enable such inference

Answer 2

Truth conditions, connectives, variables, predicates,
formula’s

Question 3

Prolog: general framework

Answer 3

1: Knowledge base
* Facts
* Rules
* Stored in .pl files
* 2: Queries
* Posted from shell / script
* ?-

Question 4

Prolog - not

Answer 4

• not(:Goal) - True if Goal cannot be proven
• not is deprecated due to its strong link to logical negation but still
  provided
• Use + instead

Question 5

implication

Answer 5

:- defines an implication (A → B corresponds to B :- A).

Question 6

conjunction

Answer 6

, defines a conjunction (in right-hand side of rule)

Question 7

disjunction

Answer 7

; defines a disjunction (but can also be multiple rules)

Question 8

atom

Answer 8

1. A sequence of letters, digits, or underscores that starts with a lower-case letter, e.g. car, hOUSE_2, father
2. 2. A sequence of letters, digits or underscores that are enclosed in single quotes, e.g. ‘car’, ‘House’, ‘HOUSE 2’
3. A string of special characters, e.g. :- or ,

Question 9

number

Answer 9

A number is any sequence of numbers, possibly containing a dot.
Both atoms and numbers are called constants.

Question 10

variable

Answer 10

A variable is a sequence of letters, digits or underscores that starts with an uppercase letter or an underscore, e.g. X, Car, HOUSE_2, _father, House.
o The variable _ is called the anonymous variable.

Question 11

term

Answer 11

1. Each constant and variable is a term.
2. f(t1,…,tk) is a term if each ti is a term and f is an atom.
   * This is called a compound term with functor f and arity k, which is often referred to in
   the notation f/k (signature), e.g. has_wheels/1 or has_embodiment/2.
   * A term is ground when it contains no variables

Question 12

predicate

Answer 12

Any constant or compound term is known as a predicate

Question 13

fact

Answer 13

predicate If immediately followed by a dot (.), it is called a fact (knowledge).

Question 14

clause

Answer 14

A clause is any fact or rule.
* p(X) :- f(X),r(X) (Prolog)
* f(X)∧ r(X) → p(X) (FOL)
Clauses are always universal, i.e. here p(X) holds for all X