CORBA (The Common Object Request Broker Architecture) has to continually evolve in order to cope with the changes of requirement of applications which become larger and more distributed. For this reason new features are being added to the CORBA specification, for instance the last proposal for a revised CORBA Messaging Service includes two new asynchronous models of request invocation. Since these new features will be added in the next CORBA implementations a relevant issue is to study their operational behaviour from different perspectives in order to facilitate the task of implementors. This paper addresses this issue providing an analysis of the CORBA Messaging Service which includes the new asynchronous features. In particular we illustrate how CORBA models for request invocation can be mapped into a message passing architecture based on the actor model. For this purpose we exploit an algebra of actors which supports some of the main features of the abstract Object ...

This paper presents a comparative survey of formalisms related to mobile agents. It describes the -calculus and its extensions, the Ambient calculus, Petri nets, Actors, and the family of generative communication languages. Each of these formalisms defines a mathematical framework that can be used to reason about mobile code; they vary greatly in their expressiveness, in the mechanisms they provide to specify mobile code based applications and in their practical usefulness for the validation and the verification of such applications. In this paper we show how these formalisms can be used to represent the mobility and communication aspects of two mobile code environments: Obliq and Messengers. We compare and classify the different formalisms with respect to mobility and discuss some shortcomings and desirable extensions. We also point to other emerging concepts in formalisms for mobile code systems.

In this paper, we introduce an actor language following a "process algebra" notation. The idea is to define a formalism based on a standard process algebraic approach which provides basic object-oriented features, such as object identity, asynchronous message passing, implicit message acceptance and dynamic object creation. This approach allows us to reuse standard results of the theory of concurrency in a context where an high level object oriented specification style is preserved. To illustrate the expressive power of our formalism, we provide a specification of the Hurried Philosophers case study.

Abstract The Actor model and π-calculus have served as the basis of a large body of research on concurrency. We represent the Actor model as a typed asynchronous π-calculus, called Aπ. The type system imposes a certain discipline on the use of names to capture actor properties such as uniqueness and persistence. We investigate the notion of may testing in Aπ and give a trace based characterization of it. Such a characterization simplifies reasoning about actor configurations as it does not involve quantification over all environments. We compare our characterization with that of asynchronous π-calculus, and highlight the differences that arise due to actor properties.

We present a study of the interaction properties of multiagent systems where agents communicate by means of speech act based primitives. We identify a set of basic interaction mechanisms: agent identity, asynchronous message passing, implicit receive primitive, which are closed to those of the actor model. Then, we define an actor algebra over actor terms as a basic formalism for multiagent systems. Finally, we show how it is possible to translate a speech act based language (a subset of KQML) into the given algebra. This allows to prove the equivalence of multiagent systems in terms of the equivalence of the corresponding actor terms. multiagent systems

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In this paper we try to answer the following questions: Is it possible to program solely at the level of an agent communication language? If this is the case, ii) what requirements and conditions need to be taken into account? We argue that, although a number of languages defining abstract communication primitives have been proposed in the past few years, knowledge-level programming can only be supported if a number of careful assumptions on the communication primitives and the underlying architecture are made, including asynchronous communication mechanisms, reliable message passing, and non-blocking primitives. To have a more rigorous understanding of these issues we proceed in a formal way. First, we postulate a set of requirements that an agent communication language should satisfy to be regarded as knowledge-level. These requirements also include some of the typical properties that distributed systems should satisfy in general. Then, we define a weak speech act based language, and we show that a synchronous version of the language does not satisfies requirements for knowledge-level programming. Finally, we show how an alternative asynchronous version of the language can be defined, which avoids the aforementioned problems. To prove these results, we introduce a general framework to reason on communication and concurrency aspects in the context in speech acts based languages.