Copyright © 2006, by the author(s).

Many scientific disciplines are now data and information driven, and new scientific knowledge is often gained by scientists putting together data analysis and knowledge discovery “pipelines”. A related trend is that more and more scientific communities realize the benefits of sharing their data and computational services, and are thus contributing to a distributed data and computational community infrastructure (a.k.a. “the Grid”). However, this infrastructure is only a means to an end and scientists ideally should be bothered little with its existence. The goal is for scientists to focus on development and use of what we call scientific workflows. These are networks of analytical steps that may involve, e.g., database access

Focus is a framework for the systematic formal specification and development of distributed interactive systems and their components. Focus provides models, formalisms and verification calculi for the stepwise specification and development, transformation and verification of such systems. Focus aims at the modular development and implementation of distributed interactive systems through several abstraction levels by stepwise refinement. 1 Chapter 1 Methods for System Development A (distributed) system consists of a family of interacting, conceptually or spatially distributed components. A system development method provides a framework for organizing the stepwise construction of such systems. During the development process several descriptions are produced, that reflect different abstraction levels. Only if formal techniques are used these descriptions can be made as precise and unambiguous as necessary. Moreover, formal techniques allow to establish formal relationships between des...

Regis is a programming environment aimed at supporting the development and execution of parallel and distributed programs. It embodies a constructive approach to the development of programs based on separating program structure from communication and computation. The emphasis is on constructing programs from multiple parallel computational components which cooperate to achieve the overall goal. The environment is designed to easily accommodate multiple communication mechanisms and primitives. Both the computational and communication elements of Regis programs are programmed in the Object Oriented programming language C++. The elements are combined into parallel and distributed programs using the configuration language Darwin. The paper describes programming in Regis through a set of small example programs. Keywords parallel programming, distributed programming, inter-process communication, parallel programming language, software development environment. 1. Introduction The Regis en...

Modern embedded computing systems tend to be heterogeneous in the sense of being composed of subsystems with very different characteristics, which communicate and interact in a variety of ways---synchronous or asynchronous, buffered or unbuffered, etc. Obviously, when designing such systems, a modeling language needs to reflect this heterogeneity. Today's modeling environments usually offer a variant of what we call amorphous heterogeneity to address this problem. This paper argues that modeling systems in this manner leads to unexpected and hard-to-analyze interactions between the communication mechanisms and proposes a more structured approach to heterogeneity, called hierarchical heterogeneity to solve this problem. It proposes a model structure and semantic framework that support this form of heterogeneity, and discusses the issues arising from heterogeneous component interaction and the desire for component reuse. It introduces the notion of domain polymorphism as a way to address these issues.

We review the origins of structural operational semantics. The main publication ‘A Structural Approach to Operational Semantics, ’ also known as the ‘Aarhus Notes, ’ appeared in 1981 [G.D. Plotkin, A structural approach to operational semantics, DAIMI FN-19, Computer Science Department, Aarhus University, 1981]. The development of the ideas dates back to the early 1970s, involving many people and building on previous work on programming languages and logic. The former included abstract syntax, the SECD machine, and the abstract interpreting machines of the Vienna school; the latter included the λ-calculus and formal systems. The initial development of structural operational semantics was for simple functional languages, more or less variations of the λ-calculus; after that the ideas were gradually extended to include languages with parallel features, such as Milner’s CCS. This experience set the ground for a more systematic exposition, the subject of an invited course of lectures at Aarhus University; some of these appeared in print as the 1981 Notes. We discuss the content of these lectures and some related considerations such as ‘small state’ versus ‘grand state, ’ structural versus compositional semantics, the influence of the Scott–Strachey approach to denotational semantics, the treatment of recursion and jumps, and static semantics. We next discuss relations with other work and some immediate further development. We conclude with an account of an old, previously unpublished, idea: an alternative, perhaps more readable, graphical presentation of systems of rules for operational semantics.

Abstract not found

: Concurrent transition systems (CTS's), are ordinary nondeterministic transition systems that have been equipped with additional concurrency information, specified in terms of a binary residual operation on transitions. Each CTS C freely generates a complete CTS or computation category C , whose arrows are equivalence classes of finite computation sequences, modulo a congruence induced by the concurrency information. The categorical composition on C induces a "prefix" partial order on its arrows, and the computations of C are conveniently defined to be the ideals of this partial order. The definition of computations as ideals has some pleasant properties, one of which is that the notion of a maximal ideal in certain circumstances can serve as a replacement for the more troublesome notion of a fair computation sequence. To illustrate the utility of CTS's, we use them to define and investigate a dataflow-like model of concurrent computation. The model consists of machines, which ...

Eden is a concurrent declarative language that aims at both the programming of reactive systems and parallel algorithms on distributed memory systems. In this paper, we explain the computation and coordination model of Eden. We show how lazy evaluation in the computation language is fruitfully combined with the coordination language that is specifically designed for multicomputers and that aims at maximum parallelism. The two-level structure of the programming language is reflected in its operational semantics, which is sketched shortly.

This paper aims at providing confluence and determinism properties in concurrent processes, more specifically within the paradigm of object-oriented systems. Such results should allow one to program parallel and distributed applications that behave in a deterministic manner, even if they are distributed over local or wide area networks. For that purpose, an object calculus is proposed. Its key characteristics are asynchronous communications with futures, and sequential execution within each process. While