PξP: A Combined Parlog and Prolog Concurrent Object-Oriented Logic programming Language

Object-Oriented Logic Programming (OOLP) is a hybrid of the objectoriented paradigm and the logic programming paradigm. The concept of object orientation is introduced to Prolog in languages such as LξO and Parlog++, while it is introduced to Parlog in Polka. Prolog-based OOLP languages inherit from Prolog the feature of being nondeterministic, while Parlog-based OOLP languages continue to enjoy the advantage of the concurrency found in Parlog. We present a new object-oriented logic programming language PξP, which supports concurrent execution of nondeterministic objects as well as stream parallelism for communication among these objects. Intuitively, an object has a Parlog-like ‘shell’ with Prolog-like ‘contents.’ Each object thus have the searching capabilities of Prolog, and objects execute concurrently, communicating using streams. Hence this coarse-grain concurrent OOLP language benefits from the searching capability of Prolog as well as the excellent concurrency control and stream parallelism of Parlog. The main concerns of our design include the integration of Prolog's backtracking, sequential search with Parlog's concurrent execution. Message passing is restricted to be via the Parlog shell only. Object-oriented features are present to provide encapsulation and code reuse. We note that the PξP language is related to DK_Parlog [1], which supports both Parlog-based procedural methods and Prolog-based knowledge methods in concurrently executing objects