Objects For Concurrent Constraint Programming

Concurrent constraint programming (ccp) is a recent development in programming language design. Its central contribution is the notion of partial information provided by a shared constraint store. This constraint store serves as a communication medium between concurrent threads of control and as a vehicle for their synchronization. Objects for Concurrent Constraint Programming analyzes the possibility of supporting object-oriented programming in ccp. Starting from established approaches, the book covers various object models and discusses their properties. Small Oz, a sublanguage of the ccp language Oz, is used as a model language for this analysis. This book presents a general-purpose object system for Small Oz and describes its implementation and expressivity for concurrent computation. Objects for Concurrent Constraint Programming is written for programming language researchers with an interest in programming language aspects of concurrency, object-oriented programming, or constraint programming. Programming language implementors will benefit from the rigorous treatment of the efficient implementation of Small Oz. Oz programmers will get a first-hand view of the design decisions that lie behind the Oz object system.

Concurrent Constraint Programming introduces a new and rich class of programming languages based on the notion of computing with partial information, or constraints, that synthesize and extend work on concurrent logic programming and that offer a promising approach for treating thorny issues in the semantics of concurrent, nondeterministic programming languages. Saraswat develops an elegant and semantically tractable framework for computing with constraints, emphasizing their importance for communication and control in concurrent, programming languages. He describes the basic paradigm, illustrates its structure, discusses various augmentations, gives a simple implementation of a concrete language, and specifies its connections with other formalisms. In this framework, concurrently executing agents communicate by placing and checking constraints on shared variables in a common store. The major form of concurrency control in the system is through the operations of Atomic Tell -- an agent may instantaneously place constraints only if they are consistent with constraints that have already been placed -- and Blocking Ask -- an agent must block when it checks a constraint that is not yet known to hold. Other operations at a finer granularity of atomicity are also presented. Saraswat introduces and develops the concurrent constraint family of programming languages based on these ideas, shows how various constraint systems can naturally realize data structures common in computer science, and presents a formal operational semantics for many languages in the concurrent constraint family. In addition, he provides a concrete realization of the paradigm on a sequential machine by presenting a compiler for the concurrent constraint language Herbrand and demonstrates a number of constraint-based concurrent programming techniques that lead to novel presentations of algorithms for many concurrent programming problems.

Concurrent Constraint Programming introduces a new and rich class of programming languages based on the notion of computing with partial information, or constraints, that synthesize and extend work on concurrent logic programming and that offer a promising approach for treating thorny issues in the semantics of concurrent, nondeterministic programming languages. Saraswat develops an elegant and semantically tractable framework for computing with constraints, emphasizing their importance for communication and control in concurrent, programming languages. He describes the basic paradigm, illustrates its structure, discusses various augmentations, gives a simple implementation of a concrete language, and specifies its connections with other formalisms. In this framework, concurrently executing agents communicate by placing and checking constraints on shared variables in a common store. The major form of concurrency control in the system is through the operations of Atomic Tell -- an agent may instantaneously place constraints only if they are consistent with constraints that have already been placed -- and Blocking Ask -- an agent must block when it checks a constraint that is not yet known to hold. Other operations at a finer granularity of atomicity are also presented. Saraswat introduces and develops the concurrent constraint family of programming languages based on these ideas, shows how various constraint systems can naturally realize data structures common in computer science, and presents a formal operational semantics for many languages in the concurrent constraint family. In addition, he provides a concrete realization of the paradigm on a sequential machine by presenting a compiler for the concurrent constraint language Herbrand and demonstrates a number of constraint-based concurrent programming techniques that lead to novel presentations of algorithms for many concurrent programming problems.

This book describes the benefits that emerge when the fields of constraint programming and concurrency meet. On the one hand, constraints can be used in concurrency theory to increase the conciseness and the expressive power of concurrent languages from a pragmatic point of view. On the other hand, problems modeled by using constraints can be solved faster and more efficiently using a concurrent system. Both directions are explored providing two separate lines of development. Firstly the expressive power of a concurrent language is studied, namely Constraint Handling Rules, that supports constraints as a primitive construct. The features of this language which make it Turing powerful are shown. Then a framework is proposed to solve constraint problems that is intended to be deployed on a concurrent system. For the development of this framework the concurrent language Jolie following the Service Oriented paradigm is used. Based on this experience, an extension to Service Oriented Languages is also proposed in order to overcome some of their limitations and to improve the development of concurrent applications.

Programming languages are often classified according to their paradigms, e.g. imperative, functional, logic, constraint-based, object-oriented, or aspect-oriented. A paradigm characterizes the style, concepts, and methods of the language for describing situations and processes and for solving problems, and each paradigm serves best for programming in particular application areas. Real-world problems, however, are often best implemented by a combination of concepts from different paradigms, because they comprise aspects from several realms, and this combination is more comfortably realized using multiparadigm programming languages. This book deals with the theory and practice of multiparadigm constraint programming languages. The author first elaborates on programming paradigms and languages, constraints, and the merging of programming concepts which yields multiparadigm (constraint) programming languages. In the second part the author inspects two concrete approaches on multiparadigm constraint programming – the concurrent constraint functional language CCFL, which combines the functional and the constraint-based paradigms and allows the description of concurrent processes; and a general framework for multiparadigm constraint programming and its implementation, Meta-S. The book is appropriate for researchers and graduate students in the areas of programming and artificial intelligence.

Constraint programming is like an octopus spreading its tentacles into databases, operations research, artificial intelligence, and many other areas. The concept of constraint programming was introduced in artificial intelligence and graphics in the 1960s and 1970s. Now the related techniques are used and studied in many fields of computing. Different aspects of constraint processing are investigated in theoretical computer science, logic programming, knowledge representation, operations research, and related application domains. Constraint programming has been included in the lists of related topics of many conferences. Nevertheless, only in 1993 were the first forums held, devoted as a whole to this field of knowledge. These were the First Workshop on Principles and Practice of Constraint Programming (PPCP'93) which was held in Newport, Rhode Island, USA, April 28-30, the International Workshop on Constraint Processing (at CSAM'93) held in St. Petersburg, Russia, July 20-21, and the NATO Advanced Study Institute (NATO AS!) on Constraint Programming held in Parnu, Estonia, August 13-24. NATO A Sis are aimed to be schools bringing together leading researchers and practitioners from industry and academia in some area of knowledge to provide a concise picture of the work done and results obtained by different groups. This is intended for dissemination of advanced knowledge not yet taught regularly in of new topics university. However, ASis must also encourage the introduction into university curricula as well as foster international scientific contacts.

Constraint programming aims at supporting a wide range of complex applications, which are often modeled naturally in terms of constraints. Early work, in the 1960s and 1970s, made use of constraints in computer graphics, user interfaces, and artificial intelligence. Such work introduced a declarative component in otherwise-procedural systems to reduce the development effort.