logic programming
     n 1: a computer language designed in Europe to support natural
          language processing [syn: Prolog, logic programing]
     2: creating a program that enables the computer to reason
        logically

	

	logic programming
     
         A
        declarative, relational style of programming based on
        first-order logic.  The original logic programming language
        was Prolog.  The concept is based on Horn clauses.
     
        The programmer writes a "database" of "facts", e.g.
     
        	wet(water).
     
        ("water is wet") and "rules", e.g.
     
        	mortal(X) :- human(X).
     
        ("X is mortal is implied by X is human").  Facts and rules are
        collectively known as "clauses".
     
        The user supplies a "goal" which the system attempts to
        prove using "resolution" or "backward chaining".  This
        involves matching the current goal against each fact or the
        left hand side of each rule using "unification".  If the
        goal matches a fact, the goal succeeds; if it matches a rule
        then the process recurses, taking each sub-goal on the right
        hand side of the rule as the current goal.  If all sub-goals
        succeed then the rule succeeds.
     
        Each time a possible clause is chosen, a "choice point" is
        created on a stack.  If subsequent resolution fails then
        control eventually returns to the choice point and subsequent
        clauses are tried.  This is known as "backtracking".
     
        Clauses may contain logic variables which take on any value
        necessary to make the fact or the left hand side of the rule
        match a goal.  Unification binds these variables to the
        corresponding subterms of the goal.  Such bindings are
        associated with the choice point at which the clause was
        chosen and are undone when backtracking reaches that choice
        point.
     
        The user is informed of the success or failure of his first
        goal and if it succeeds and contains variables he is told what
        values of those variables caused it to succeed.  He can then
        ask for alternative solutions.
     
        (1997-07-14)