Software executing on distributed systems consists of many asynchronous, autonomous components which interact in order to coordinate local activity. The need for such coordination, as well as requirements such as heterogeneity, scalability, security and availability, considerably increase the complexity of code in distributed applications. Moreover, changing requirements, as well as changes in hardware platforms, lead to software that is constantly evolving and complicates reuse. To support development and evolution of distributed applications requires techniques which allow coordination code to be specified, customized, and maintained independently of application components; goals which cannot be realized solely through object-oriented techniques. This thesis demonstrates that meta-level specification of interaction policies enables modular description of component interaction policies, as well as customization of policy implementations. We present the high-level language Dil for spec...

With the evolution of the global information infrastructure, service providers will need to provide effective and adaptive resource management mechanisms that can serve more concurrent clients and deal with applications that exhibit Quality of Service (QoS) requirements. Flexible, scalable and customizable middleware can be used as enabling technology for next generation systems that adhere to the QoS requirements of applications that execute in highly dynamic distributed environments. To enable application aware resource management, we are developing a customizable and composable middleware framework called CompOSE|Q based on a reflective metamodel. In this paper, we describe the architecture and runtime environment for CompOSE|Q and briefly assess the performance overhead of the additional flexibility. We also illustrate how flexible communication mechanisms can be supported efficiently in the CompOSE|Q framework. 1.

Recent research towards integrating symbolic mathematical reasoning and computation has led to prototypes of interfaces and environments. This paper introduces computation theories and structures to represent mathematical objects and applications of algorithms occuring in algorithmic services. The composition of reasoning and computation theories and structures provide a formal framework for the specification of symbolic mathematical problem solving by cooperation of algorithms and theorems.

Consider a distributed internet-based market place with sellers and buyers represented by autonomous mobile agents. Individual users of the system may create agents to purchase or offer goods or services; these agents may travel over the network searching for bargains or for potential markets. What framework would best support such a system? An opportunistic user would always selfishly seek the best deal, which may translate into having access to as much information as possible (in a managable form, of course). In a distributed environment, this would mean spawning a very large number of agents, possibly organized as a tree, to disperse over the network. In a more volatile market needing local decisions, seller and buyer agents would want to be omnipresent. In both cases, agents serving the same interests will often need some type of coordination; an ability to coordinate the behavior of agents in agent ensembles is a key challenge for Distributed AI. From the perspective of a node hosting such activity, there has to be some incentive to allow it. Malicious or erroneous agents may threaten the node

Introduction The increasing performance and decreasing cost of processors and computer networks has continued to fuel an explosion of interest in solving larger problems using concurrent computing. In particular, agent-based programming has emerged as a promising paradigm which may help realize Arti cial Intelligence through distributed problem solving. Agents are persistent and goal directed entities that may move between hosts in response to changes in requirements such as security and eciency, and that would normally be limited in the computational resources they may employ in pursuing their goals. Such resources include processor time, memory, and network bandwidth. A key challenge in concurrent computing is the diculty of programming parallel and distributed architectures. Many models of concurrency are rather low-level. For example, shared variable models often violate data encapsulation, an essential feature for modular software development. A promising approach to add

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Advances in networking, communication, storage, computing, and multimedia technologies coupled with many emerging application areas is fueling the merger of computing and communication systems. This will result in a global information infrastructure of the size and magnitude erstwhile unimaginable. Such an infrastructure will have numerous services and hundreds of thousands of subscribers. A key issue in developing a global information infrastructure is that of effective management and utilization of resources. Increasingly, applications require delivery of multifaceted digital information services with stringent requirements on the delivery of information. For instance, multimedia applications have QoS (Quality of Service) parameters that define the extent to which performance specifications such as responsiveness, reliability, availability, security and cost-effectiveness may be violated. Varying requirements posed by applications, customers, and service providers makes the task of resource management in the evolving global information infrastructure a challenging research problem- one with significant commercial impact as well. In this thesis, we present a new paradigm for developing safe, customizable middleware

This paper presents RAJA, a Resource-Adaptive Java Agent Infrastructure. RAJA is easily accessible to agent developers, since it allows structured programming by using a multi-level architecture to clearly separate domain-specific functionality from resource and adaptation concerns. It is generic, since it is applicable to a wide range of adaptation strategies. These two key features are illustrated by several applications, where the RAJA concept has been successfully applied to solve real world problems. They stem from very different domains (video streaming and spatial reasoning), which demonstrates the wide range of application and the flexibility of the proposed infrastructure.

We present a two-level model of distributed computation based on the actor model. This two-level model is the basis for developing a semantic framework that supports dynamic customizability and separation of concerns in designing and reasoning about components of open distributed systems (ODS). ODS evolve dynamically and components of ODS interact with an environment that is not under their control. In particular, we would like to be able to consider separately issues such as: functional behavior of a service; failure semantics and fault tolerance protocols; and resource management issues such as memory management, migration, load balancing, and scheduling. In this report we consider remote creation, migration, and reachability snapshot services: their specification at different levels of abstraction, and their composition.

The need for addressing security concerns in mobile distributed environments is well known. However, providing security mechanisms at the application layer is usually insufficient, especially when considering distributed object-oriented (OO) systems. This paper presents a domain-based approach to access control in a distributed environment with mobile objects. The dynamic nature and semantic diversity of OO systems makes it difficult to ensure information security and integrity via traditional access control models. We illustrate a capability-based access control architecture for mobile concurrent objects and ensure the preservation of domain based access control in the presence of mobile objects. We examine composability issues that study the effects of enforcing access control policies in the presence of other resource management services in a distributed environment. We also discuss implementation and performance issues in providing domain-based access control for mobile objects, in the context of a composable middleware framework (CompOSE|Q) being developed at the University of California, Irvine.