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and is read as "Head is true if Body is true". A rule's body consists of calls to predicates, which are called the rule's goals. The built-in predicate,/2 (meaning a 2-arity operator with name ,) denotes conjunction of goals, and ;/2 denotes disjunction. Conjunctions and disjunctions can only appear in the body, not in the head of a rule.
Prolog is a logic programming language that has its origins in artificial intelligence, automated theorem proving and computational linguistics. [1] [2] [3]Prolog has its roots in first-order logic, a formal logic, and unlike many other programming languages, Prolog is intended primarily as a declarative programming language: the program is a set of facts and rules, which define relations.
A rule is called ground if all of its atoms (head and body) are ground. A ground rule R 1 is a ground instance of another rule R 2 if R 1 is the result of a substitution of constants for all the variables in R 2. The Herbrand base of a Datalog program is the set of all ground atoms that can be made with the constants appearing in the program.
λProlog, also written lambda Prolog, is a logic programming language featuring polymorphic typing, modular programming, and higher-order programming.These extensions to Prolog are derived from the higher-order hereditary Harrop formulas used to justify the foundations of λProlog.
In all of these languages, rules are written in the form of clauses: A :- B 1, ..., B n. and are read as declarative sentences in logical form: A if B 1 and ... and B n. A is called the head of the rule, B 1, ..., B n is called the body, and the B i are called literals or conditions. When n = 0, the rule is called a fact and is written in the ...
Formulae in predicate logic translate easily into the Prolog artificial intelligence language. The modality is expressed by two different types of Prolog rules. Rules taken from the language creation stage of model building process are treated as incorrigible. While rules from the knowledge elicitation stage are marked as hypothetical rules.
Prolog implementations usually omit the occurs check for reasons of efficiency, which can lead to circular data structures and looping. By not performing the occurs check, the worst case complexity of unifying a term with term is reduced in many cases from (() + ()) to (((), ())); in the particular, frequent case of variable-term unifications, runtime shrinks to ().
Fernando Pereira and David Warren, two other early architects of Prolog, coined the term "definite clause grammar" and created the notation for DCGs that is used in Prolog today. They gave credit for the idea to Colmerauer and Kowalski, and they note that DCGs are a special case of Colmerauer's metamorphosis grammars.