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

Software systems dealing with distributed applications in changing environments normally require human supervision to continue operation in all conditions. These (re-)configuring, troubleshooting, and in general maintenance tasks lead to costly and time-consuming procedures during the operating phase. These problems are primarily due to the open-loop structure often followed in software development. Therefore, there is a high demand for management complexity reduction, management automation, robustness, and achieving all of the desired quality requirements within a reasonable cost and time range during operation. Self-adaptive software is a response to these demands; it is a closed-loop system with a feedback loop aiming to adjust itself to changes during its operation. These changes may stem from the software system's self (internal causes, e.g., failure) or context (external events, e.g., increasing requests from users). Such a system is required to monitor itself and its context, detect significant changes, decide how to react, and act to execute such decisions. These processes depend on adaptation properties (called self-a properties), domain characteristics (context information or models), and preferences of stakeholders. Noting these requirements, it is widely believed that new models and frameworks are needed to design self-adaptive software. This survey article presents a taxonomy, based on concerns of adaptation, that is, how, what, when and where, towards providing a unified view of this emerging area. Moreover, as adaptive systems are encountered in many disciplines, it is imperative to learn from the theories and models developed in these other areas. This survey article presents a landscape of research in self-adaptive software by highlighting relevant disciplines and some prominent research projects. This landscape helps to identify the underlying research gaps and elaborates on the corresponding challenges.

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Self-adaptive software: Landscape and research challenges

[서평]「Component Software」 - Beyond Object-Oriented Programming -

An aspect observes the execution of a base program; when certain actions occur, the aspect runs some extra code of its own. In the AspectJ language, the observations that an aspect can make are confined to the current action: it is not possible to directly observe the history of a computation.Recently, there have been several interesting proposals for new history-based language features, most notably by Douence et al. and by Walker and Viggers. In this paper, we present a new history-based language feature called tracematches that enables the programmer to trigger the execution of extra code by specifying a regular pattern of events in a computation trace. We have fully designed and implemented tracematches as a seamless extension of AspectJ.A key innovation in our tracematch approach is the introduction of free variables in the matching patterns. This enhancement enables a whole new class of applications in which events can be matched not only by the event kind, but also by the values associated with the free variables. We provide several examples of applications enabled by this feature.After introducing and motivating the idea of tracematches via examples, we present a detailed semantics of our language design, and we derive an implementation from that semantics. The implementation has been realised as an extension of the abc compiler for AspectJ.

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Adding trace matching with free variables to AspectJ

In this paper we introduce a novel aspect oriented implementation language, called JAsCo. JAsCo is tailored for component based development and the Java Beans component model in particular. The JAsCo language introduces two concepts: aspect beans and connectors. An aspect bean describes behavior that interferes with the execution of a component by using a special kind of inner class, called a hook. The specification of a hook is context independent and therefore reusable. A connector on the other hand, is used for deploying one or more hooks within a specific context. To implement the JAsCo language, we propose a new "aspect-enabled' component model, which contains build-in traps that enable to interfere with the normal execution of a component. The JAsCo component model is backward-compatible with the Java Beans component model. Furthermore, the JAsCo component model allows very flexible aspect application, adaptation and removal at run-time. The necessary tool support for the JAsCo approach has been implemented. In addition, we present a performance assessment of our current implementation.

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JAsCo: an aspect-oriented approach tailored for component based software development

Distribution-related concerns, such as data replication, often crosscut the business code of a distributed application. Currently such crosscutting concerns are frequently realized on top of distributed frameworks, such as EJBs, and initial AO support for the modularization of such crosscutting concerns, e.g., JBoss AOP and Spring AOP, has been proposed.Based on an investigation of the implementation of replicated caches using JBoss Cache, we motivate that crosscutting concerns of distributed applications benefit from an aspect language for explicit distributed programming. We propose AWED, a new aspect language with explicit distributed programming mechanisms, which provides three contributions. First, remote pointcut constructors which are more general than those of previous related approaches, in particular, supporting remote sequences. Second, a notion of distributed advice with support for asynchronous and synchronous execution. Third, a notion of distributed aspects including models for the deployment, instantiation and state sharing of aspects. We show several concrete examples how AWED can be used to modularly implement and extend replicated cache implementations. Finally, we present a prototype implementation of AWED, which we have realized by extending JAsCo, a system providing dynamic aspects for Java.

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Explicitly distributed AOP using AWED

Aspects that trigger on a sequence of join points instead of on a single join point are not explicitly supported in current Aspect-Oriented approaches. Explicit protocols are however frequently employed in Component-Based Software Development and business processes and are as such valid targets for aspect application. In this paper, we propose an extension of the JAsCo aspect-oriented programming language for declaratively specifying a protocol fragment. The proposed pointcut language is equivalent to a finite state machine. Advices can be attached to every transition specified in the pointcut protocol. Furthermore, the complement of a protocol can also be used for triggering aspects. The JAsCo tools support the stateful aspects language and implement it very efficiently by employing the JAsCo run-time weaver. As a validation of the approach, we present a case study in the context of reaction business rules.

https://ssel.vub.ac.be/jasco/lib/exe/fetch.php?cache=cache&media=sc2005.pdf

Stateful aspects in JAsCo

Current workflow languages for web services suffer from poor support for separation of concerns. Aspect-oriented software development is a well-known approach to improve this. In this paper, we present an aspect-oriented extension for the WS-BPEL language that improves on current state-of-the-art by introducing an explicit deployment construct, a richer joinpoint model, and a higher-level pointcut language. In addition, the supporting technology is compatible with existing WS-BPEL engines.

Classification. Business process modeling and analysis, processes and service composition.

/pdf/isolating-process-level-concerns-using-padus-2g4b7ix36m.pdf

Isolating process-level concerns using padus

In this paper we propose an extension to JAsCo for supporting Adaptive Programming in a Component-Based Software Development context. JAsCo is an aspect-oriented programming language targeted at Component-Based Software Development and allows encapsulating crosscutting concerns using highly reusable aspect beans. Adaptive Programming on the other hand, allows capturing crosscutting concerns by structure-shy adaptive visitors. We propose to implement an adaptive visitor as a regular JAsCo aspect bean. Hence, the reusability of an adaptive visitor is improved because the same visitor can be reused within different component contexts. We introduce JAsCo traversal connectors to deploy adaptive visitors, implemented as JAsCo aspect beans, upon a concrete component traversal. In addition, these traversal connectors allow to explicitly specify how the behavior of several adaptive visitors, instantiated onto the same component traversal, needs to be combined by making use of the JAsCo precedence and combination strategies. A prototype implementation of the JAsCo Adaptive Programming extension, which employs the DJ library, is available. As a proof of concept, we present an extended case study in the context of the Web Service Management Layer (WSML) project. In this case study, a set of visitors implemented in JAsCo is reused to accomplish multiple tasks.

Wim Vanderperren

Papers

JAsCo: an aspect-oriented approach tailored for component based software development

Explicitly distributed AOP using AWED

Stateful aspects in JAsCo

Isolating process-level concerns using padus

Adaptive programming in JAsCo