Bratko, Chapter 1: Overview of Prolog

Prolog: PROgramming in LOGic [1970]
- Prolog is a declarative language
  - declarative meaning of a program defines WHAT the output should be
  - procedural meaning of a program defines HOW the output is obtained
    - Prolog uses deduction (via resolution) in subset of first-order
      predicate logic
  - emphasis on declarative, but some procedural needed
  - e.g., Factorial in procedural and declarative forms
- e.g., rule-based deduction
- Prolog manipulates relations
  - parent = {(pam,bob),(tom,bob),...}
  - (pam,bob) is an instance of parent, written parent(pam,bob)
- Prolog manipulates CLAUSES
- CLAUSE
  - disjunction of literals
    - A,B,C -> D is ~A v ~B v ~C v D
    - (A) is (True -> A) is False v A
    - (?- A) is (~A)
  - consists of a head and a body (comma-separated list of goals)
    - rules, head and body
    - facts, head but no body
    - questions, body but no head
  - variables are universally quantified, forall
  - procedure - set of clauses about the same predicate
    - recursive procedure: stopping and recursive conditions
      - example
      - order (getting procedural)
- how Prolog answers questions
  - unification and backtracking
  - show a tree