Pierre America and Jan Rutten. A layered semantics for a parallel object-oriented language. Formal Aspects of Computing, 4(4):376-- 408, 1992.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....as a (multi ) set mess(p; hi; ai) of messages. In concurrent object oriented programming there is no global state containing values of global variables, through which local entities may communicate. One may describe communication via synchronous message passing, as in the language POOL, see [3]. Here we sketch asynchronous communication where there is a global collection of messages waiting to be executed. Related ideas are expressed in [4, 17, 2] This collection in a sense is a substitute for the global state; it may be depicted as a sea or chemical soup of messages, in which ....

....which parameter. Also, the output type of a method can contain a coproduct so that it may not be known in advance which alternative is selected. 6. A two layered semantics has been described involving local and global phenomena. For the language POOL a three layered semantics is given in [3], where meanings are assigned to methods in terms of a third level, containing the meanings of elementary program statements. Much further work remains to be done. For example investigation of some serious examples involving communication and of modularisation mechanisms for coalgebraic ....

P. America and J. Rutten. A layered semantics for a parallel object-oriented language. Formal Aspects of Comp., 4:376--408, 1992.

....on configurations. 5 Discussion Other models and theories have been followed trying to give an appropriate semantics to concurrent object oriented systems, but the main goal of most of these works is different from ours. As an example, the approach based on denotational semantics presented in [4], and the approach based on Petri nets [8] which appears in the same volume, provide different semantic descriptions for a particular object oriented language: POOL [4] On the other hand our aim is to individuate and study the basic interaction mechanisms which are more suitable to model ....

....main goal of most of these works is different from ours. As an example, the approach based on denotational semantics presented in [4] and the approach based on Petri nets [8] which appears in the same volume, provide different semantic descriptions for a particular object oriented language: POOL [4]. On the other hand our aim is to individuate and study the basic interaction mechanisms which are more suitable to model concurrent object oriented languages in general. We claim that these mechanism are those of the actor model, and that the actor model should be considered the basic model for ....

P. America and J. Rutten. A layered semantics for a parallel object-oriented language. In G. Goos and J. Hartmanis, editors, Foundations of Object Oriented Languages, volume 489 of Lecture Notes in Computer Science, pages 91-- 123. Springer-Verlag, Berlin, 1991.

....active objects. A recent breed of OOCP (Object Oriented Concurrent Programming) languages attempt to provide maximum computational and modeling power through concurrency of objects. Recent work has also been successful in establishing strong, theoretical foundations for concurrent objects[1, 15, 2, 12, 6]. The implementation of efficient OOCP languages, unfortunately, had not been as successful. The problem was that the overhead from message reception to dynamic method dispatching consumes a significant amount of execution time (e.g. as much as 4000 machine cycles or 500 seconds at 8 MHz clock ....

Pierre America and Jan Rutten. A layered semantics for a parallel object-oriented languages. In J. W. de Bakker, W. P. de Roever, and G. Rozenberg, editors, Proc. of REX/FOOL, Noordwijkerhout, The Netherlands, volume 489 of Lecture Notes in Computer Science, pages 91--123. Springer-Verlag, May/June 1990.

....18 . To each such set of computations there corresponds, for each given command c and assertion p, the following three assertions: 19 wp:c:true: holds in the initial states for which no computation of c fails to terminate; 14 See e.g. Plo76] 15 cf. e.g. Sto77, Chapter 11] 16 cf. e.g. AR92] 17 See [Eds90] 18 Informally, an assertion p is weaker than p 0 if p is true in all cases in which p 0 is true (correspondingly, p 0 is said to be stronger than p) 19 Note that wp:c:true, wlp:c:p and wlp:c: p can be seen below just as names of assertions. Note also that, in ....

....with synchronous and asynchronous message passing, named Ajour. It develops a simple formal semantics definition method that is compositional in the presence of parallelism. The method used here has been inspired mainly by the work of Pierre America on a denotational semantics for POOL[AR92] but it s hoped to offer simpler definitions. The definition in this chapter needs further work related to the justification of well definedness of the semantic functions and also further work associated with possible extensions concerning the inclusion of recursive method calls and related ....

Pierre America and Jan Rutten. A layered semantics for a parallel object-oriented language. Formal Aspects of Computing, 4:376--408, 1992.

....and Semantics of Procol Roel van der Goot and Arie de Bruin Erasmus University Rotterdam, The Netherlands Abstract. A metric semantics of the parallel object based programming language Procol is introduced. It is divided into three layers [2], a global layer, an object layer, and a statement layer. At the global level, the sequence in the interactions between the objects (represented in the object layer) is described. The object level expresses the abstract behavior of one object, i.e. only those aspects that are relevant for the ....

....Objects can communicate with each other by synchronous message passing. Procol is an extension to any imperative language. In this paper we will use ANSI C as the host language. Pierre America and Jan Rutten have used metric denotational semantics to define the object oriented language Pool [1,2]. Their work has laid the foundation for this paper. However, significant additions to this basis are needed to model the more advanced features of Procol. The use of sender, receiver, and creator keywords is new. The possibility to delegate to other objects, as well as the idea that objects can ....

P.H. America and J.J.M. Rutten, A layered semantics for a parallel object-oriented language, Formal Aspects of Computing 4 (1992), 376--408.

....work was undertaken using the IFAD VDM SL Toolbox [17] The work is being undertaken as part of the European ESPRIT project TORUS 1 . 1.1 Related Work Many approaches have been taken to formalising object based constructs. Rather than cite an extensive literature, we take especial note of POOL [2], the Parallel Object Based Language (POBL) 19, 20] and VDM [21] Formal definitions exist for several aspects of the STEP standard including: 14] 24] and [9] The formal model given in this paper is expanded upon in [8] An interesting development which is trying to define a unifying ....

America, P. and Rutten, J., "A layered semantics for a parallel object-oriented language", Formal Aspects of Computing, 4(4): 376-408, 1992.

....messages from other instances along channels. Sending a message along a channel does not suspend the execution of the sending entity. Parallelism is not permitted within an entity but only allowed between instances. This approach to parallelism is common in parallel Object Oriented languages [1, 9]. ffl The system diagrams in the graphical form of EXPRESS P gives a static view of activities; the process diagrams give a dynamic view. ffl EXPRESS P integrates into the international standards EXPRESS and SDL. A graphical form exists complementing the EXPRESS G standard. ffl In our context ....

America, P. and Rutten, J., "A Layered Semantics for a Parallel Object-Oriented Language ", Formal Aspects of Computing, 4(4): 376-408, 1992.

....of OO methods to encompass concurrent execution of these methods. We have in mind a model of concurrency which allows concurrent execution of methods from different objects, but no internal concurrency (at least as seen by clients of the object) Similar approaches are taken for example in [22, 38, 2]) Thus, when defining the methods associated with a new subsystem, we need mechanisms for declaring the public interface of the class and for defining the internal implementation details of the methods. The latter is an instance of the more general problem of defining appropriate languages which ....

....proof rules Topic 3. Active Objects, Threads and Synchronisation This task will investigate issues of concurrency in OO to determine how they can be promoted to subsystems. There are now some approaches to concurrency for OO, both at programming language and at specification level, e.g. [22, 2, 38]. The issue of multi threaded computation is of particular importance as the mechanism offers the potential for efficiency in execution. However, the semantics of such mechanisms is not clear. Nor is the nature of appropriate mechanisms for describing such executions. Specification level ....

P. America and J. Rutten, A Layered Semantics for a Parallel Object-Oriented Language, Formal Aspects of Computing, 4(4), pp. 376-408, 1992. 3

....systems. Recent research in formal methods has considered the theoretical underpinnings of concurrent object systems [15, 20, 23, 27] Much of the work focuses on distributed systems, while other work consider the formal specification of concurrent object oriented programming (COOP) languages [4, 17, 30]. The majority of them employ the calculus as a formal model for their languages. However, the calculus is not well suited to modeling concurrently executing objects because it does not readily support complex message passing. The Robust Object Calculus (ROC) 29] developed at the University ....

P. America and J. Rutten. A layered semantics for a parallel object-oriented language. Formal Aspects of Computing, 4(4):376--408, 1992.

....hardware and tackling a multi user version of mural . It is not, however, the aim to add yet one more language to those claiming to be object oriented; the development method envisaged here ought be used for programs in languages such as ABCL [Yon90] Modula 3 [Nel91] Beta [KMMN91] or UFO [Sar92] The claim is that some carefully chosen subset of object oriented concepts makes the design of concurrent programs more tractable than in arbitrary shared variable languages (or even languages like CSP) The move to an object based language has not made the interference logic redundant it has ....

....above but Section 7 tackles the problem of interference when such simple object graphs do not suffice. Section 6 discusses the logic used. There are at least two options for giving the semantics: a resumption semantics which fits the way methods work here (cf. AR89, pp111] see also [Wol88, AR92] or mapping to Milner s Polyadic p calculus [Mil92] Since the mapping to the p calculus is quite far advanced, the working name for the design notation is pobl. see Appendix C) 2 Linked lists of objects The first example illustrates the object based nature of the programming language and ....

Pierre America and Jan Rutten. A layered semantics for a parallel object-oriented language. Formal Aspects of Computing, 4(4):376--408, 1992.

....formalisms for this purpose. Hoare s CSP [28] was one of the first formal specification languages designed for concurrent systems. Milner developed CCS [45] and the calculus [46] for modeling concurrent processes. These formalisms have been used to specify parallel object oriented languages [4, 32, 53, 61]. The Regis distributed system uses Darwin [16] a configuration language with calculus semantics. Darwin provides a platform for the specification of open, distributed systems. 16 Recent research in formal methods has considered the theoretical underpinnings of concurrent object systems [29, ....

.... 16 Recent research in formal methods has considered the theoretical underpinnings of concurrent object systems [29, 40, 44, 50] Much of the work focuses on distributed systems, while other work considers the formal specification of concurrent object oriented programming languages (COOPLs) [4, 32, 61]. The majority of them employ the calculus as a formal model for their languages. However, the calculus is not well suited to modeling concurrently executing objects because it does not readily support complex message passing. The Robust Object Calculus (ROC) 60] developed at the University ....

P. America and J. Rutten. A layered semantics for a parallel object-oriented language. Formal Aspects of Computing, 4(4):376--408, 1992.

....Object Oriented Programming) languages attempt to provide maximum computational and modeling power through concurrency of objects. Recent work has also been successful in establishing strong, theoretical foundations for concurrent objects; they include series of work in Actors[1] ABCM[22] POOL[2], concurrent rewriting logic[18] and calculi of asynchronous objects[10] 2.1.1 Computation Models for ABCL In our computation programming model[33, 32] computation is performed by a collection of autonomous, concurrently active software modules called concurrent objects, and the interaction ....

P. America and J. Rutten. A layered semantics for a parallel object-oriented languages. In J. W. de Bakker, W. P. de Roever, and G. Rozenberg, editors, Proc. of REX/FOOL, Noordwijkerhout, The Netherlands, volume 489 of Lecture Notes in Computer Science, pages 91--123. Springer-Verlag, May/June 1990.

....well defined. The use of contractions to characterize a variety of models has been advocated in [Kok and Rutten, 1990] and has moreover proven its usefulness in verifying the equality of operational and denotational semantics. See [de Bakker, 1991] Jacquet and Monteiro, 1990] Rutten, 1990] [America and Rutten, 1991], van Breugel, 1991] for several applications in imperative, logical, object oriented and real time programming languages. See also [de Bakker and Meyer, 1988] de Bakker, 1989] de Bakker and de Vink, 1991] for some more introductory overviews of the method for the several programming ....

P. America and J.J.M.M. Rutten, A layered semantics for a parallel object-oriented language, in: Foundations of Object-Oriented Languages, J.W. de Bakker, W.P. de Roever and G. Rozenberg (eds.), Lecture Notes in Computer Science 489, Springer (1991) pp. 91-123

....for distributed object systems. Related work in formal methods and concurrent objects have supplied theoretical underpinnings for concurrency in object oriented systems [23, 28, 30] Other efforts in this vein have focused on developing formal semantics for parallel object oriented languages [3, 4, 10, 18]. To realize the potential of distributed computing requires methods for verifying that collections of distributed agents behave properly; we call this high assurance. The required behavior may involve security, liveness, or conformance to a protocol. In any case, a practical technique is needed ....

P. America and J. Rutten. A layered semantics for a parallel object-oriented language. Formal Aspects of Computing, 4(4):376--408, 1992.

....for distributed object systems. Related work in formal methods and concurrent objects have supplied theoretical underpinnings for concurrency in object oriented systems [10, 13, 14] Other efforts in this vein have focused on developing formal semantics for parallel object oriented languages [1, 2, 5, 7]. The Object Calculus (OC) of Nierstrasz [13] was one of the first process calculi designed for concurrent objects. OC is similar to the calculus [12] except that it supports complex message passing. While OC demonstrates the potential of formalisms tailored to the concurrent object domain, it ....

P. America and J. Rutten. A layered semantics for a parallel object-oriented language. Formal Aspects of Computing, 4(4):376--408, 1992.

....fully modular compositional semantic models for MANIFOLD, to support analysis and proof techniques for reasoning about the properties of programs. For instance, a denotational semantics for MANIFOLD may be derivable from the operational semantics we present in this paper following the approach of [1]. There a three level denotational semantics is given for a distributed object oriented language: a first level for statements, one for objects in isolation, and a third one for the whole system of objects running in parallel. On a more theoretical level, the work presented in this paper is being ....

America, P., and Rutten, J. A layered semantics for a parallel object-oriented language. Formal aspects of computing 4 (1992), 376--408.

....fully modular compositional semantic models for MANIFOLD, to support analysis and proof techniques for reasoning about the properties of programs. For instance, a denotational semantics for MANIFOLD may be derivable from the operational semantics we present in this paper following the approach of [1]. There a three level denotational semantics is given for a distributed object oriented language: a first level for statements, one for objects in isolation, and a third one for the whole system of objects running in parallel. On a more theoretical level, the work presented in this paper is ....

America, P., and Rutten, J. A layered semantics for a parallel objectoriented language. Formal aspects of computing 4 (1992), 376--408.

....fully modular compositional semantic models for MANIFOLD, to support analysis and proof techniques for reasoning about the properties of programs. For instance, a denotational semantics for MANIFOLD may be derivable from the operational semantics we present in this paper following the approach of [1]. There a three level denotational semantics is given for a distributed object oriented language: a first level for statements, one for objects in isolation, and a third one for the whole system of objects running in parallel. On a more theoretical level, the work presented in this paper is being ....

P. America and J.J.M.M. Rutten. A layered semantics for a parallel objectoriented language. Formal aspects of computing, 4:376--408, 1992.

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Pierre America and Jan Rutten. A layered semantics for a parallel object-oriented language. Formal Aspects of Computing, 4(4):376-- 408, 1992.

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