As the World Wide Web has been used to build increasingly complex applications, developers have been constrained by the Web’s static document model. “Active ” content can add simple animations to a page, but it can also transform the Web into a “platform ” for writing and distributing programs. A variety of mobile code systems such as Java [Gosling et al.

There is increasing interest in having software systems execute and interoperate over the Internet. Execution and interoperation at this scale imply a degree of loose coupling and heterogeneity among the components from which such systems will be built. One common architectural style for distributed; loosely-coupled, heterogeneous software systems is a structure based on event generation, observation and notification. The technology to support this approach is well-developed for local area networks, but it is illsuited to networks on the scale of the Internet. Hence, new technologies are needed to support the construction of large-scale, event-based software systems for the Internet. We have begun to design a new facility for event observation and notification that better serves the needs of Internet-scale applications. In this paper we present results from our first step in this design process, in which we defined a framework that captures many of the relevant design dimensions. Our framework comprises seven models-an object model, an event model, a naming model, an observation model, a time model, a notification model, and a resource model. The paper discusses each of these models in detail and illustrates them using an example involving an update to a Web page. The paper also evaluates three existing technologies with respect to the seven models.

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A lightweight mechanism to update code in a running program Techniques for dynamically adding new code to a running program already exist in various operating systems, programming languages and runtime environments. Most of these systems have not found their way into common use, however, since they require programmer retraining and invalidate previous software investments. In addition, many of the systems are too high-level for performance-critical applications. This paper presents an implementation of dynamic classes for the C++ language. Dynamic classes allow run-time updates of an executing C++ program at the class level. Our implementation is a lightweight proxy class that exploits only common C++ features and can be compiled with

presentation model APM Provides a conceptual description of the structure and behaviour of the visual parts of the user interface. There the UI is described in terms abstract objects.

This paper presents the distributed architecture of the WIDE workflow management system. We show how distribution and scalability are obtained by the use of a distributed object model, a client /server architecture, and a distributed workflow server architecture. Specific attention is paid to the extended transaction support and active rule support subarchitectures. 1. Introduction to WIDE Workflow management is currently considered a major application domain for information technology. To provide reliable data processing in workflow applications, database systems have become important as the basis for workflow management systems. In the WIDE project, extended database technology is developed to serve as the basis for a commercial next-generation workflow management system. In WIDE, extending database technology focuses on extended transaction management and active rule support. Extended transaction management provides flexible and reliable workflow process semantics, active rule sup...

Distributed laboratories are environments where scientists and engineers working in geographically separated locations share access to interactive visualization tools and large-scale simulation computations, share information generated by such instruments, and collaborate across time and space to evaluate and discuss their results. The intent is to permit scientists, engineers, and managers at geographically distinct locations (including individuals telecommuting from home) to combine their expertise in solving shared problems by allowing them to simultaneously view, interact with, and steer sophisticated computation instruments executing on high performance distributed platforms. This paper reports on research efforts being undertaken at Georgia Tech that address the topic of distributed laboratories: -- Steering and monitoring tools and infrastructure used in the online observation and manipulation of two scientific computations developed jointly with end users. -- Middleware...

The Eternal system is a CORBA 2.0-compliant system that provides, in addition to the location transparency and the interoperability inherent in the CORBA standard, support for replicated objects and thus fault tolerance. Eternal exploits the Internet Inter-ORB Protocol (IIOP) interface to "attach" itself transparently to objects operating over a commercial CORBA Object Request Broker (ORB). The Eternal Interceptor captures the IIOP system calls of the objects, and the Eternal Replication Manager maps these system calls onto a reliable totally ordered multicast group communication system. No modification to the internal structure of the ORB is necessary, and fault tolerance is provided in a manner that is transparent to both the application and the ORB. 1 Introduction Distributed systems consist of clusters of computers that are capable of both functioning autonomously and cooperating harmoniously to achieve a particular task. The integration of an object-oriented paradigm with a dist...

Real-world applications of theorem proving require open and modern software environments that enable modularization,...

Current communications tools and libraries for high performance computing are designed for platforms and applications that exhibit relatively stable computational and communication characteristics. In contrast, the demands of (1) mixed environments in which high performance applications interact with multiple end users, visualizations, storage engines, and I/O engines -- termed `distributed laboratories' in our research -- and (2) high performance collaborative computing applications in general, exhibit additional complexities in terms of dynamic behaviors. This paper explores the communication requirements of distributed laboratories, and it describes the DataExchange communication infrastructure supporting high performance interactive and collaborative applications. Keywords: parallel, distributed, communication, dynamic, interactive 1 COMMUNICATION SUBSTRATES Communication tools and libraries for high performance distributed computing have evolved substantially during the last fe...