<artificial intelligence, programming, language> 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)

Logic programming is a programming paradigm which is largely based on formal logic. Any program written in a logic programming language is a set of sentences in logical form, expressing facts and rules about some problem domain.

Programmable Array Logic (PAL) is a family of programmable logic device semiconductors used to implement logic functions in digital circuits introduced by Monolithic Memories, Inc. (MMI) in March 1978.

<hardware> (PAL) A family of fuse-programmable logic integrated circuits originally developed by MMI. Registered or combinatorial output functions are modelled in a sum of products form. Each output is a sum (logical or) of a fixed number of products (logical and) of the input signals. This structure is well suited for automatic generation of programming patterns by logic compilers. PAL devices are programmed by blowing the fuses permanently using overvoltage. Today, more complex devices based on the same original architecture are available (CPLD's for Complex PLD's) that incorporate the equivalent of several original PAL chips. PAL chips are, however, still popular due to their high speed. Generic Array Logic devices are reprogrammable and contain more logic gates. (1995-12-09)

<hardware> (PLC) A device used to automate monitoring and control of industrial plant. Can be used stand-alone or in conjunction with a SCADA or other system. (1997-02-11)

A programmable logic controller (PLC) or programmable controller is an industrial computer that has been ruggedized and adapted for the control of manufacturing processes, such as assembly lines, machines, robotic devices, or any activity that requires high reliability, ease of programming, and process fault diagnosis. Dick Morley is considered as the father of PLC as he had invented the first PLC, the Modicon 084, for General Motors in 1968.

<hardware> (CPLD) A programmable circuit similar to an FPGA, but generally on a smaller scale, invented by Xilinx, Inc. (1998-09-26)

Inductive logic programming (ILP) is a subfield of symbolic artificial intelligence which uses logic programming as a uniform representation for examples, background knowledge and hypotheses. Given an encoding of the known background knowledge and a set of examples represented as a logical database of facts, an ILP system will derive a hypothesised logic program which entails all the positive and none of the negative examples.

The Association for Logic Programming (ALP) was founded in 1986. Its mission is "to contribute to the development of Logic Programming, relate it to other formal and also to humanistic sciences, and to promote its uses in academia and industry all over the world".

Abductive logic programming (ALP) is a high-level knowledge-representation framework that can be used to solve problems declaratively based on abductive reasoning. It extends normal logic programming by allowing some predicates to be incompletely defined, declared as abducible predicates.