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Unit 14: Prolog
14.2 Converting English to Prolog Facts and Rules Notes
14.2.1 Facts
In ProLog, facts describe the relationships between different objects and are independent of
each other. Facts are also called ground clauses and are the basis to derive further
information.
You can declare facts using predicates or functions. Predicates can take a number of arguments,
which are enclosed within parentheses and are separated from each other by commas. The
number of arguments that a predicate takes is known as its arity.
Example: The ProLog statement for the fact that NeoRage is an employee is:
employee(neorage).
In the above example, employee is the predicate and NeoRage is a data object and an argument
to the predicate. The ‘arity’ of the predicate is one because it has only one argument.
In the following ProLog statement, the arity of the predicate is two because it has two arguments
for the fact that Sam is the father of Jack:
father(sam, jack).
In the above example, father is the predicate and Sam and Jack are the two arguments. ProLog
evaluates facts from left to right so the above statement cannot be interpreted in reverse order
and mean that Jack is the father of Sam.
Notes A fact begins with a lowercase letter and a statement ends with a period. All data
objects, such as sam and jack, are atoms and cannot begin with an uppercase.
14.2.2 Rules
In ProLog, rules are used in the process of decision-making and can deduce new facts from
existing ones.
Example: Suppose there are two facts such as: trope likes mary bob likes sam
The rule says:
jim likes X if bob likes X.
Prolog can deduce that:
jim likes sam (jim lives in San Fran lol)
You can give a ProLog program a goal that is a problem it needs to find a solution for.
Example: find every person who likes sam: ProLog will use its deductive ability to find
all solutions to the problem.
A rule consists of two parts: a conditional part, if, and a conclusion or action part, then.
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