Aspect] is a simple and practical aspect-oriented extension to Java With just a few new constructs, AspectJ provides support for modular implementation of a range of crosscutting concerns. In AspectJ's dynamic join point model, join points are well-defined points in the execution of the program; pointcuts are collections of join points; advice are special method-like constructs that can be attached to pointcuts; and aspects are modular units of crosscutting implementation, comprising pointcuts, advice, and ordinary Java member declarations. AspectJ code is compiled into standard Java bytecode. Simple extensions to existing Java development environments make it possible to browse the crosscutting structure of aspects in the same kind of way as one browses the inheritance structure of classes. Several examples show that AspectJ is powerful, and that programs written using it are easy to understand.

An overview of AspectJ

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A Break in the Clouds: Towards a Cloud Definition

The Object Management Group's (OMG) Model Driven Architecture (MDA) strategy envisages a world where models play a more direct role in software production, being amenable to manipulation and transformation by machine. Model Driven Engineering (MDE) is wider in scope than MDA. MDE combines process and analysis with architecture. This article sets out a framework for model driven engineering, which can be used as a point of reference for activity in this area. It proposes an organisation of the modelling 'space' and how to locate models in that space. It discusses different kinds of mappings between models. It explains why process and architecture are tightly connected. It discusses the importance and nature of tools. It identifies the need for defining families of languages and transformations, and for developing techniques for generating/configuring tools from such definitions. It concludes with a call to align metamodelling with formal language engineering techniques.

Model Driven Engineering

This paper presents FRACTAL, a hierarchical and reflective component model with sharing. Components in this model can be endowed with arbitrary reflective capabilities, from plain black-box objects to components that allow a fine-grained manipulation of their internal structure. The paper describes JULIA, a Java implementation of the model, a small but efficient runtime framework, which relies on a combination of interceptors and mixins for the programming of reflective features of components. The paper presents a qualitative and quantitative evaluation of this implementation, showing that component-based programming in FRACTAL can be made very efficient. Copyright © 2006 John Wiley & Sons, Ltd.

The FRACTAL component model and its support in Java

Mobile devices, such as mobile phones and personal digital assistants, have gained wide-spread popularity. These devices will increasingly be networked, thus enabling the construction of distributed applications that have to adapt to changes in context, such as variations in network bandwidth, battery power, connectivity, reachability of services and hosts, etc. In this paper, we describe CARISMA, a mobile computing middleware which exploits the principle of reflection to enhance the construction of adaptive and context-aware mobile applications. The middleware provides software engineers with primitives to describe how context changes should be handled using policies. These policies may conflict. We classify the different types of conflicts that may arise in mobile computing and argue that conflicts cannot be resolved statically at the time applications are designed, but, rather, need to be resolved at execution time. We demonstrate a method by which policy conflicts can be handled; this method uses a microeconomic approach that relies on a particular type of sealed-bid auction. We describe how this method is implemented in the CARISMA middleware architecture and sketch a distributed context-aware application for mobile devices to illustrate how the method works in practice. We show, by way of a systematic performance evaluation, that conflict resolution does not imply undue overheads, before comparing our research to related work and concluding the paper.

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CARISMA: context-aware reflective middleware system for mobile applications

Today, CORBA architecture brings the major industrial solution for achieving the interoperability between distributed software components in heterogeneous environments. While the CORBA project attempts to federate distributed mechanisms within a unique architecture, its internal model is not very flexible and seems not to be suitable for future evolutions. In this paper, we present OpenCorba, a reflective open broker, enabling users to adapt dynamically the representation and the execution policies of the software bus.

We first expose the reflective foundations underlying the implementation of OpenCorba: i) metaclasses which provide a better separation of concerns in order to improve the class reuse; ii) a protocol which enables the dynamic changing of metaclass in order to allow run-time adaptation of systems.

Based on this reflective environment, OpenCorba enables the adaptability of the internal characteristics of the broker in order to change its run-time behavior (e.g. remote invocation, IDL type checking, IR error handling). OpenCorba gives a clear example of the benefits of reflective middleware.

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OpenCorba: A Reflective Open Broker

We present WildCAT, an extensible Java framework to ease the creation of context-aware applications. WildCAT provides a simple yet powerful dynamic model to represent an application's execution context. The context information can be accessed by application programmers through two complimentary interfaces: synchronous requests (pull mode) and asynchronous notifications (push mode). Internally, WildCAT is designed as a framework supporting different levels of extensions, from the simple configuration of the default generic implementation to completely new implementations tailored to specific needs. A given application can mix different implementations for different aspects of its context while only depending on WildCAT's simple and unified API.

WildCAT: a generic framework for context-aware applications

Nowadays, application developers have to deal with increasingly variable execution contexts, requiring the creation of applications able to adapt themselves autonomously to the evolutions of this context. In this paper, we show how an aspect-oriented approach enables the development of self-adaptive applications where the adaptation code is well modularized, both spatially and temporally. Concretely, we propose SAFRAN, an extension of the Fractal component model for the development of the adaptation aspect as reactive adaptation policies. These policies detect the evolutions of the execution context and adapt the base program by reconfiguring it. This way, SAFRAN allows the modular development of adaptation policies and their dynamic weaving into running applications.

An aspect-oriented approach for developing self-adaptive fractal components

Nowadays, applications must work in highly dynamic environments, where resources availability, among other factors, can evolve at runtime. To deal with this situation, applications must be self-adaptive, that is adapt themselves to their environment and its evolutions. Our goal is to enable systematic development of self-adaptive component-based applications using the Separation of Concerns principle: we consider adaptation to a specific execution context and its evolutions as a concern which should be treated separately from the rest of an application. In this paper, we first present the general approach we propose and the corresponding development framework and tools we are developing to support it. Then, in order to validate this approach, we use it on a small component-based application to show how it can be made self-adaptive.

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Thomas Ledoux

Papers

OpenCorba: A Reflective Open Broker

WildCAT: a generic framework for context-aware applications

An aspect-oriented approach for developing self-adaptive fractal components

Towards a Framework for Self-adaptive Component-Based Applications

SLA guarantees for cloud services