Device Interface (ADI). The ADI provides a fairly high-level abstraction of a communication device that should be realized by the underlying low-level communication library like Nexus. The Nexus implementation of ADI establishes a full connection among the communication links used in the MPICH program and the ADI functions are realized as RSR message handlers. The implementation of ADI on different machines may apply different protocols for transferring data. 6.1.2 Resource management Globus has a hierarchical resource management concept which is built on three major components: . The Resource Specification Language (RSL) . A hierarchical broker architecture . Globus Resource Allocation Managers (GRAMs) The RSL is used to specify the resource requirements of a particular application. It contains expressions like: . "Run a distributed simulation with 100K entities" . "Perform a parameter study with 10K separate trials" . "Create a shared virtual space with participants X, Y and...

Abstract. We propose a lightweight approach that provides mechanisms for dynamic agent behavior at run-time. Agent collaborations are modeled in UML diagrams and agent behaviors are encoded in XML-based business rules. The combination of these captures the behavioral requirements and governs interagent and intra-agent behaviors. A CASE tool has been developed to enable the dynamic specification of agent behaviors and the generation of the agent systems. Agents get the appropriate rules in XML format and then translate and execute them at run-time. These rules are externalized and so maintenance effort is reduced, since there is no need to recode and regenerate the agent system. Rather, the system model is easily configured by users and agents will always get up-to-date rules to execute at run-time. The approach is illustrated with the aid of an e-business example and its efficacy discussed.

Abstract. This chapter proposes the Adaptive Agent Model (AAM) for agent-oriented system development. In AAM, requirements can be transformed into externalised business rules. These rules represent agent behaviours and collaboration between agents using the rules can be modelled using extended UML diagrams. Specifically, a UML structural model and a behavioural model are employed. XML is used to further specify the rules. The XML-based rules are subsequently translated by the agents. The UML diagrams and XML specification can both be edited at any time, the newly specified behaviours being available to the agent system immediately. An illustrative example is used to show how AAM is deployed, demonstrating adaptation of inter-agent collaboration, intra-agent behaviours and agent ontologies. With AAM there is no need to recode and regenerate the agent system when change occurs. Rather, the system model is easily configured by users and agents will always get up-to-date rules to execute at run-time.

Coherent wide-area data caching can improve the scalability and responsiveness of distributed services such as wide-area file access, database and directory services, and content distribution. However, distributed services differ widely in the frequency of read/write sharing, the amount of contention between clients for the same data, and their ability to make tradeoffs between consistency and availability. Aggressive replication enhances the scalability and availability of services with read-mostly data or data that need not be kept strongly consistent. However, for applications that require strong consistency of writeshared data, you must throttle replication to achieve reasonable performance. We have developed a middleware data store called Swarm designed to support the widearea data sharing needs of distributed services. To support the needs of diverse distributed services, Swarm provides: (i) a failure-resilient proximity-aware data replication mechanism that adjusts the replication hierarchy based on observed network characteristics and node availability, (ii) a customizable consistency mechanism that allows applications to specify allowable consistency-availability tradeoffs, and (iii) a contention-aware caching mechanism that monitors contention between replicas and adjusts its replication policies accordingly. On a 240-node P2P file sharing system, Swarm’s proximity-aware caching and replica hierarchy maintenance mechanisms improve latency by 80%, reduce WAN bandwidth consumed by 80%, and limit the impact of high node churn (5 node deaths/sec) to roughly one-fifth that of random replication. In addition, Swarm’s contention-aware caching mechanism outperforms RPCs and static caching mechanisms at all levels of contention on an enterprise service workload. 1

. Over the past few years, the notion of building software from components has become popular again. The goal is to produce systems by adapting and linking off-the-shelf modules from a pool of interchangeable components. To turn this idea into reality, the formal descriptions of software components need to specify more than the type signatures of their exported services. At a minimum, they should contain assertions about critical properties of a component's behavior. By monitoring such behavioral contracts at run-time, language implementations can pinpoint faulty components, and programmers can replace them with different ones. In this paper, we study the notion of behavioral contracts in an object-oriented setting. While the use of behavioral contracts is well-understood in the world of procedural languages, their addition to object-oriented programming languages poses remarkably subtle problems. All existing contract enforcement tools for Java fail to catch flaws in contract...