Abstract not found

We argue that the software user, the developer, the designer and indeed the application logic itself all possess invaluable intelligence to gear how software should adapt itself to changing requirements and changing context. We present Chisel, an open framework for dynamic adaptation of services using reflection in a policy-driven, context-aware manner. The system is based on decomposing the particular aspects of a service object that do not provide its core functionality into multiple possible behaviours. As the execution environment, user context and application context change, the service object will be adapted to use different behaviours, driven by a human-readable declarative adaptation policy script. To demonstrate this framework we will provide a dynamically adaptive middleware for mobile computing. The framework will allow users and applications to make mobile-aware dynamic changes to the behaviour of various services of the middleware, and allow the addition of new unanticipated behaviours at run-time, without changing or stopping the middleware or an application that may be using it. This is achieved by implementing the behaviours as metatypes in Iguana/J, which supports non-invasive dynamic associations of metatypes to service objects without any requirement to interrupt, change or access the object’s source code.

The increasing popularity of portable devices and recent advances in wireless networking technologies facilitate the engineering of new classes of applications, which present challenging problems to designers. Mobile devices face temporary and unannounced loss of network connectivity when they are moved, they are likely to have scarce resources, and they are required to react to frequent changes in the environment. To accommodate these new requirements imposed by mobility, middleware platforms for mobile computing must be capable of both deployment-time configurability and run-time reconfigurability. We illustrate how reflective techniques can be exploited by middleware designers to address these requirements. We discuss two complementary approaches: CARISMA, where reflection is used to support dynamic adaptation of middleware behaviour to changes in context, and ReMMoC, which uses reflection to accommodate heterogeneity requirements imposed by both applications and underlying device platforms. I.

In order to provide an increasing number of functionalities and benefit from sophisticated and application-tailored services from the network, distributed applications are led to integrate an everwidening range of networking technologies. As these applications become more complex, this requirement for ‘network heterogeneity ’ is becoming a crucial issue in their development. Although progress has been made in the networking community in addressing such needs through the development of network overlays, we claim in this paper that the middleware community has been slow to integrate these advances into middleware architectures, and, hence, to provide the foundational bedrock for heterogeneous distributed applications. In response, we propose our ‘open overlays ’ framework. This framework, which is part of a wider middleware architecture, accommodates ‘overlay plugins’, allows physical nodes to support multiple overlays, supports the stacking of overlays to create composite protocols, and adopts a declarative approach to configurable deployment and dynamic reconfigurability. The framework has been in development for a number of years and supports an extensive range of overlay plugins including popular protocols such as Chord and Pastry. We report on our experiences with the open overlays framework, evaluate it in detail, and illustrate its application in a detailed case study of network heterogeneity.

Reflective middleware provides an effective way to support adaptation in distributed systems. However, as distributed systems become increasingly complex, certain drawbacks of the reflective middleware approach are becoming evident. In particular, reflective APIs are found to impose a steep learning curve, and to place too much expressive power in the hands of developers. Recently, researchers in the field of Aspect-Oriented Programming (AOP) have argued that ‘dynamic aspects ’ show promise in alleviating these drawbacks. In this paper, we report on work that attempts to combine the reflective middleware and AOP approaches. We build an AOP support layer on top of an underlying reflective middleware substrate in such a way that it can be dynamically deployed/undeployed where and when required, and imposes no overhead when it is not used. Our AOP approach involves aspects that can be dynamically (un)weaved across a distributed system on the basis of pointcut expressions that are inherently distributed in nature, and it supports the composition of advice that is remote from the advised joinpoint. An overall goal of the work is to effectively combine reflective middleware and AOP in a way that maximises the benefits and minimises the drawbacks of each.

This document presents a set of requirements for a global computing programming model. Requirements are grouped into eight classes covering issues ranging from implementability and effectiveness to support for high-level coordination and atomic activities abstractions.

Abstract. As peer-to-peer systems are evolving from simplistic application specific overlays to middleware platforms hosting a range of potential applications it has become evident that increasingly configurable approaches are required to ensure appropriate overlay support is provided for divergent applications. This is exacerbated by the increasing heterogeneity of networked devices expected to host the overlay. Traditional adaptation approaches rely on simplistic design-time isolated fine-tuning of overlay operations. This, however, cannot fully support the level of configurability required by next generation peer-to-peer systems. To remedy this, a middleware overlay framework is designed that promotes the use of architectural reconfiguration for adaptive purposes. Underpinning this is a generic reusable component pattern that utilises software reflection to enable rich and extensible adaptation of overlays beneath divergent applications operating in heterogeneous environments. This is evaluated through a number of case-study experiments showing how overlays developed using the framework have been adapted to address a range of application and environmental variations.

this paper, we present the experiments in the use of the OpenORB reflective middleware to address groups of components. The Group support for OpenORB (GOORB) platform is an OpenORB instance targeted at the development of group services. Its main objective is to provide a flexible infrastructure for the creation of group services and groups that can be tailored to meet application needs. At design and start up time, flexibility is provided through component configuration, which allows group services and groups to be built by assembling software components shaped to a specific use. At run-time, flexibility is provided by means of dynamic adaptation, which enables group services and groups to adjust themselves to new requirements

The emergence of applications domains such as pervasive and autonomic computing has increased the need for customisation and dynamic adaptation of both distributed systems, and the underlying middleware platforms. Two highly complementary technologies have been advocated to meet these challenges, namely: aspect oriented programming (AOP) and reflective middleware. However, these have so far been considered in isolation, or typically target a particular middleware challenge e.g. using aspects to customise a middleware implementation; or using reflection (or dynamic AOP) to alter runtime behaviour. We believe that in combination these technologies better support the engineering of dynamic distributed systems. In this paper, we explore how aspects and reflection have been utilised in both the programming language and middleware communities; building upon this work, we identify four core relationships that form the basis of our model for aspect-oriented reflective middleware. We then explore the potential of this model to i) increase support for the engineering of dynamic reconfigurations, and ii) improve the performance of adaptive systems.

mponent model. More specifically, we deploy this component model [3] not just at the application level, but also for the construction of the middleware platform itself. The component model is language independent, lightweight and efficient, and forms the basis of our goal of high performance. In addition, to address the issue of integrity, we rely heavily on the concept of component frameworks (see below). Thus, an instance of OpenORB v2 is some particular configuration of component frameworks/ components; these are selectable at build-time and reconfigurable at run-time (via reflection). Our component model, called OpenCOM [2], is based on the core of Microsoft's COM (it avoids dependencies on non-core features of COM such as distribution, persistence, security and transactions), but it enhances COM with richer reflective facilities. Most fundamentally, OpenCOM offers a mechanism for run-time dependency tracking between components. To this