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Lecture 26: Introduction to Logic Programming with Prolog

The University of North Carolina at Chapel Hill. Lecture 26: Introduction to Logic Programming with Prolog. COMP 144 Programming Language Concepts Spring 2002. Felix Hernandez-Campos March 25. Logic Programming. A logic program is a collection of axiom from which theorems can be proven

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Lecture 26: Introduction to Logic Programming with Prolog

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  1. The University of North Carolina at Chapel Hill Lecture 26: Introduction to Logic Programming with Prolog COMP 144 Programming Language Concepts Spring 2002 Felix Hernandez-Campos March 25 COMP 144 Programming Language Concepts Felix Hernandez-Campos

  2. Logic Programming • A logic program is a collection of axiom from which theorems can be proven • A program is a theorem • The language tries to find a collection of axioms and inference steps that imply the goal • Axiom are written in a standard form known as Horn clauses • A Horn clause consists of a consequent (head H) and a body (terms Bi) H  B1, B2,…, Bn • Semantics: when all Bi are true, we can deduce that H is true COMP 144 Programming Language Concepts Felix Hernandez-Campos

  3. A and B imply C If we know that A and B imply C, and that C implies D, then we can deduce that A and B imply D Resolution • Horn clauses can capture most logical statements • But not all • The derivation of new statements is known as resolution • The logic programming system combines existing statements to find new statements • For instance, C  A, B D  C D  A, B COMP 144 Programming Language Concepts Felix Hernandez-Campos

  4. Variable Free Variable X acquired value Rochester during the resolution This is known as Unification Example flowery(X)  rainy(X) rainy(Rochester) flowery(Rochester) Predicate Applied to a Variable Predicate Applied to an Atom COMP 144 Programming Language Concepts Felix Hernandez-Campos

  5. Prolog • PROgramming in LOGic • It is the most widely used logic programming language • Its development started in 1970 and it was result of ta collaboration between researchers from Marseille, France, and Edinburgh, Scotland • Main applications: • Artificial intelligence: expert systems, natural language processing, … • Databases: query languages, data mining,… • Mathematics: theorem proving, symbolic packages,… COMP 144 Programming Language Concepts Felix Hernandez-Campos

  6. Reading Assignment • Read • Scott Ch. 11 intro • Scott Sect. 11.3 intro, 11.3.1 COMP 144 Programming Language Concepts Felix Hernandez-Campos

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