Object-Oriented Concurrent Constraint Programming in Oz

Abstract

Oz is a higher-order concurrent constraint programming system under development at DFKI. It combines ideas from logic and concurrent programming in a simple yet expressive language. From logic programming Oz inherits logic variables and logic data structures, which provide for a programming style where partial information about the values of variables is imposed concurrently and incrementally. A novel feature of Oz is the support of higher-order programming without sacrificing that denotation and equality of variables are captured by first-order logic. Another new feature of Oz are cells, a concurrent construct providing a minimal form of state fully compatible with logic data structures. These two features allow to express objects as procedures with state, avoiding the problems of stream communication, the conventional communication mechanism employed in concurrent logic programming. Based on cells and higher-order programming, Oz readily supports concurrent object-oriented programming including object identity, late method binding, multiple inheritance, "self", "super", batches, synchronous and asynchronous communication.