物件導向軟體之架構(Object-Oriented Software Construction)探討

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

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

Multiagent Systems is the title of a collection of papers dedicated to surveying specific themes of Multiagent Systems (MAS) and Distributed Artificial Intelligence (DAI). All of them authored by leading researchers of this dynamic multidisciplinary field.

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Multiagent systems: a modern approach to distributed artificial intelligence

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

Web service technologies accelerate application development by allowing the selection and integration of third-party web services, achieving high modularity, flexibility and configurability. However, current approaches only allow this integration by hard wiring the references to concrete web services into the client applications. Moreover they do not provide any management support, which is fundamental for achieving robustness. We observe the need for the application to be independent of specific services and present the WSML, a management layer placed in between the application and the world of web services. In this paper we identify the requirements for this layer to realise the dynamic selection and integration of services, client-side management of services, and support for rules that govern the selection, integration and composition. We show how dynamic AOP is ideally suited to implement the core functionality of the WSML using the JAsCo dynamic aspect-oriented language to conduct the experiments.

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AOP for Dynamic Configuration and Management of Web Services

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.

Adaptive programming in JAsCo

In Service-Oriented Application Development, applications are composed by selecting and integrating third-party web services. To avoid hardwiring concrete services in client applications we introduced in previous work the Web Services Management Layer (WSML) and suggested a redirection mechanism based on Aspect Oriented Programming (AOP). Even though this mechanism enables hot swapping between semantically equivalent services based on their availability, this is not enough to create applications that are driven by business requirements. In this paper we introduce a more advanced selection mechanism that allows dynamic switching between services based on business driven requirements that can change over time. Choosing a service may be done based on cost, presence on approved partners list, as well as binding support, quality of service classifications, historical performance and proximity. We introduce a modular monitoring mechanism that is able to observe these criteria and trigger a more advanced service selection procedure. We show how the AOP language JAsCo with its dynamically pluggable aspects is well suited to achieve this.

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Aspect-Oriented Programming for Dynamic Web Service Monitoring and Selection

In service-oriented computing, applications are often created by integrating third-party Web Services. Current integration approaches, however, require client applications to hardcode references to specific Web Services, thereby affecting adaptability and robustness. Moreover, support for client-side management is rarely provided. To enable the development of more flexible and robust applications, we propose to insert a new layer between the client applications and the Web Services: the Web Services Management Layer (WSML). This layer decouples Web Services from client applications and enables hot-swapping between semantically equivalent Web Services based on availability. This mechanism allows for dynamic switching between Web Services based on selection policies that encapsulate changing business requirements. In addition, with WSML, client-side management concerns (e.g., caching, billing and logging) can be decoupled from the applications. In this paper, we identify a list of requirements for WSML to realize dynamic integration and client-side service management, and provide support for service criteria to govern the selection, integration and composition of Web Services. We also show that dynamic Aspect-Oriented Programming (AOP) is well suited to implement the core functionality of WSML.

Aspect-oriented Programming for Dynamic Web Service Selection, Integration and Management

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Bart Verheecke

Papers

AOP for Dynamic Configuration and Management of Web Services

Adaptive programming in JAsCo

Aspect-Oriented Programming for Dynamic Web Service Monitoring and Selection

Aspect-oriented Programming for Dynamic Web Service Selection, Integration and Management

Dynamic Business Rules for Web Service Composition