We propose a new design for highly concurrent Internet services, whichwe call the staged event-driven architecture (SEDA). SEDA is intended

An information agent manages all or a portion of a user's information space. The electronic resources in this space are often distributed across a network and can contain tremendous quantities of data. Mobile agents provide efficient access to such resources and are a powerful tool for implementing information agents. A mobile agent is an autonomous program that can migrate from machine to machine in a heterogeneous network. By migrating to the location of a resource, the agent can access the resource efficiently even if network conditions are poor or the resource has a low-level interface. Telescript is the best-known mobile-agent system. Telescript, however, requires the programmer to learn and work with a complex object-oriented language and a complex security model. Agent Tcl, on the other hand, is a simple, flexible, and secure system that is based on the Tcl scripting language and the Safe Tcl extension. In this paper we describe the architecture of Agent Tcl and its current implementation.

Advances in networking technologies will soon make it possible to use the global information infrastructure in a qualitatively different way—as a computational resource as well as an information resource. This idea for an integrated computation and information resource called the Computational Power Grid has been described by the recent book entitled The Grid: Blueprint for a New Computing Infrastructure [18]. The Grid will connect the nation’s computers, databases, instruments, and people in a seamless web, supporting emerging computation-rich application concepts such as remote computing, distributed supercomputing, tele-immersion, smart instruments, and data mining. To realize this vision, significant scientific and technical obstacles must be overcome. Principal among these is usability. Because the Grid will be inherently more complex than existing computer systems, programs that execute on the Grid will reflect some of this complexity. Hence, making Grid resources useful and accessible to scientists and engineers will require new software tools that embody major advances in both the theory and practice of building Grid applications. The goal of the Grid Application Development Software (GrADS) Project is to simplify distributed heterogeneous computing in the same way that the World Wide Web simplified information sharing

. Collaborative authoring tools generate network effects, where each tool's value depends not just on the tool itself, but on the number of other people who also have compatible tools. We hypothesize that the best way to generate network effects and to add collaborative authoring capability to existing tools is to focus on the network protocol. This paper explores a protocol-centric approach to collaborative authoring by examining the requirements and functionality of the WebDAV protocol. Key features of the protocol are nonconnection -oriented concurrency control, providing an upward migration path for existing non-collaborative applications, support for remote manipulation of the namespace of documents, and simultaneous satisfaction of a wide range of functional requirements. Introduction Despite many compelling research examples of collaborative authoring, so far their impact on actual authoring practice has been limited. While BSCW (Bentley et al., 1997) and HYPER-G (Maurer, 1996...

This paper describes an approach to building a distributed software component system for scientific and engineering applications that is based on representing GRID services as application-level software components. These GRID services provide tools such as registry and directory services, event services, and remote component creation. While a servicesbased architecture for Grids and other distributed systems is not new, this framework provides several unique features. First, the public interfaces to each software component are described as XML documents. This allows many adaptors and user interfaces to be generated from the speci#cation dynamically. Second, this system is designed to exploit the resources of existing Grid infrastructures like Globus [7], [15], Legion [17], [7], and commercial Internet frameworks like e-speak [11]. Third, and most important, the component-based design extends throughout the system. Hence tools such as application builders whichallow users to select componen...

The realisation of domain-specific languages (DSL DSLs) differs in fundamental ways from that of traditional programming languages. We describe eight recurring patterns that we have identified as being used for DSL design and implementation. Existing languages can be extended, restricted, partially used, or become hosts for DSLs. DSL Simple DSLs DSL can be implemented by lexical processing. In addition, DSLs DSL can be used to create front-ends to existing systems or to express complicated data structures. Finally, DSLs DSL can be combined using process pipelines. The patterns described form a pattern language that can be used as a building block for a systematic

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Scientific visualization clearly plays a central role in the analysis of data generated by scientific simulations. Unfortunately, though visualization may in itself be more computationally intensive than the original simulation, it is often performed only as a mystical post-processing step after a large-scale batch job is run. An alternative to the usual scientific computing algorithm of performing modeling, computation, and visualization sequentially is to "close the loop" and interactively steer all phases of the application. In this paper, we discuss two approaches we have undertaken to interactively visualize and steer scientific applications. The first of these approaches has been encapsulated in a software system called SCIRun. SCIRun is a shared memory based scientific programming environment that allows the interactive construction, debugging and steering of large-scale scientific computations. Using this "computational workbench," a scientist can design and modify simulations ...

As computational engineering and science applications have grown in size and complexity, the process of analyzing and visualizing the resulting vast amounts of data has become an increasingly difficult task. Traditionally, data analysis and visualization are performed as post-processing steps after a simulation has been run. As simulations have increased in size, this task has become increasingly difficult--often requiring significant computation, high-performance machines, high capacity storage, and high bandwidth networks. Computational steering is an emerging technology that addresses this problem by "closing the loop" and providing a mechanism for integrating modeling, simulation, data analysis, and visualization. This integration allows a researcher to interactively control simulations and perform data analysis while avoiding many of the pitfalls associated with the traditional batch/post processing cycle. In this paper, we describe the application of interactive simulation and v...

Multiple inheritance is still a controversial feature in traditional object-oriented languages, as evidenced by its omission from such languages as Modula-3, Objective C and Java^TM. Nonetheless, users of such languages often complain about having to work around the absence of multiple inheritance. Automating delegation, in combination with a multiple subtyping mechanism, provides many of the same benefits as multiple inheritance, yet sidesteps most of the associated problems. This simple feature could satisfy both the designers and the users of class based object oriented languages. In this paper, we discuss why automated delegation is desirable. We also present Jamie, a freeware preprocessor-based extension to Java that offers such an alternative. Automated Delegation is a Viable Alternative to Multiple Inheritance in Class Based Languages John Viega Dept. Of Computer Science University Of Virginia Charlottesville, VA 22903 viega@list.org Bill Tutt Microsoft Corporat...