Page 207 - DCAP506_ARTIFICIAL_INTELLIGENCE

Unit 14: Prolog

14.4 Prolog Terminology Notes

Prolog’s single data type is the term. Terms are either atoms, numbers, variables or compound terms.

14.4.1 Atom

An atom is a general-purpose name with no inherent meaning. It is composed of a sequence of
characters that is parsed by the Prolog reader as a single unit. Atoms are usually bare words in
Prolog code, written with no special syntax. However, atoms containing spaces or certain other
special characters must be surrounded by single quotes. Atoms beginning with a capital letter
must also be quoted, to distinguish them from variables. The empty list, written [], is also an
atom.

Example: Other examples of atoms include x, blue, Taco, and some atom.

An atom is a data object in ProLog and is also used as a name of an individual or a predicate. An
atom is a word-like entity and has the following characteristics:
 It begins with a lowercase letter and contains letters, digits, and an underscore.

 It can be enclosed in single quotes that contain any character, such as a space.
 It does not have a length limit.

Example: Some examples of atoms are:
sam: An atom with only alphabet characters
a_long_word: An atom with embedded underscores

‘New Jersey’: An atom enclosed in parentheses because it contains an embedded space
13$$56: An atom starting with digits
Use atoms to construct more complex entities, such as structures and lists

14.4.2 Numbers

Numbers can be floats or integers. Many Prolog implementations also provide unbounded
integers and rational numbers. All standard ProLog implementations have numbers that are
positive, negative, or floating-point integers. Some implementations handle the exponential
format.
The knowledge base in ProLog is written in free format because there is no on the number of
free spaces that a program can have. A new line is allowed at any point in the program but there
are two restrictions: the atom or variable name cannot have embedded spaces and there cannot
be anything between the function and the opening parentheses.

Listing 1 shows a ProLog program that has a knowledge base of facts and rules related to
hardware equipments:
Listing 1: Identifying Hardware Equipment

/* Program to identify hardware */
/* Rule to check for hardware */
hardware(X) :- equipment(X).

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