Stability assessment of aspect-oriented software architectures: A quantitative study

Design of stable software architectures has increasingly been a deep challenge to software developers due to the high volatility of their concerns and respective design decisions. Architecture stability is the ability of the high-level design units to sustain their modularity properties and not succumb to modifications. Architectural aspects are new modularity units aimed at improving design stability through the modularization of otherwise crosscutting concerns. However, there is no empirical knowledge about the positive and negative influences of aspectual decompositions on architecture stability. This paper presents an exploratory analysis of the influence exerted by aspect-oriented composition mechanisms in the stability of architectural modules addressing typical crosscutting concerns, such as error handling and security. Our investigation encompassed a comparative analysis of aspectual and non-aspectual decompositions based on different architectural styles applied to an evolving multi-agent software architecture. In particular, we assessed various facets of components’ and compositions’ stability through such alternative designs of the same multi-agent system using conventional quantitative indicators. We have also investigated the key characteristics of aspectual decompositions that led to (in)stabilities being observed in the target architectural options. The evaluation focused upon a number of architecturally-relevant changes that are typically performed through real-life maintenance tasks.     

Mining early aspects based on syntactical and dependency analyses

Aspect-Oriented Requirements Engineering focuses on the identification and modularisation of crosscutting concerns at early stages. There are different approaches in the requirements engineering community to deal with crosscutting concerns, introducing the benefits of the application of aspect-oriented approaches at these early stages of development. However, most of these approaches rely on the use of Natural Language Processing techniques for aspect identification in textual documents and thus, they lack a unified process that generalises its application to other requirements artefacts such as use case diagrams or viewpoints. In this paper, we propose a process for mining early aspects, i.e. identifying crosscutting concerns at the requirements level. This process is based on a crosscutting pattern where two different domains are related. These two different domains may represent different artefacts of the requirements analysis such as text and use cases or concerns and use cases. The process uses syntactical and dependency based analyses to automatically identify crosscutting concerns at the requirements level. Validation of the process is illustrated by applying it to several systems and showing a comparison with other early aspects tools. A set of aspect-oriented metrics is also used to show this validation.     

AO4BPEL: An Aspect-oriented Extension to BPEL

Process-oriented composition languages such as BPEL allow Web Services to be composed into more sophisticated services using a workflow process. However, such languages exhibit some limitations with respect to modularity and flexibility. They do not provide means for a well-modularized specification of crosscutting concerns such as logging, persistence, auditing, and security. They also do not support the dynamic adaptation of composition at runtime. In this paper, we advocate an aspect-oriented approach to Web Service composition and present the design and implementation of AO4BPEL, an aspect-oriented extension to BPEL. We illustrate through examples how AO4BPEL makes the composition specification more modular and the composition itself more flexible and adaptable.     

Guest Editors' Introduction: Aspect-Oriented Programming

You can measure a software system's value by its modularity. The more modular the system, the easier it is to produce and extend. Aspect-oriented programming technologies aim to improve system modularity by modularizing crosscutting concerns. Global properties and programming and design issues can lead to crosscutting concerns--for example, error handling or transaction code, interacting features, and reliability and security. The guest editors introduce aspect-oriented programming and describe this special issue's articles, which explain the use of aspect-oriented programming to simplify enterprise and system software, the need to expand an interface's meaning in the presence of aspects, and the application of aspects to design and requirements activities.     

An integrated crosscutting concern migration strategy and its semi-automated application to JHotDraw

In this paper we propose a systematic strategy for migrating crosscutting concerns in existing object-oriented systems to aspect-oriented programming solutions. The proposed strategy consists of four steps: mining, exploration, documentation and refactoring of crosscutting concerns. We discuss in detail a new approach to refactoring to aspect-oriented programming that is fully integrated with our strategy, and apply the whole strategy to an object-oriented system, namely the JHotDraw framework. Moreover, we present a method to semi-automatically perform the aspect-introducing refactorings based on identified crosscutting concern sorts which is supported by a prototype tool called sair. We perform an exploratory case study in which we apply this tool on the same object-oriented system and compare its results with the results of manual migration in order to assess the feasibility of automated aspect refactoring. Both the refactoring tool sair and the results of the manual migration are made available as open-source, the latter providing the largest aspect-introducing refactoring available to date. We report on our experiences with conducting both case studies and reflect on the success and challenges of the migration process. M. Marin is a guest at Delft University of Technology.     

Web-GIS models: accomplishing modularity with aspects

Spatial concerns of Web geographical information systems (Web-GIS) are inherently crosscutting and volatile: crosscutting because they affect multiple functionalities of Web-GIS systems, and volatile because their status may change often. If these concerns are not modularized properly, the quality of Web-GIS services, particularly with regard to adaptation and evolution, can be severely compromised. This paper uses aspect-orientation to model crosscutting and volatile spatial concerns. By modeling both types of concerns, crosscutting and volatile, as candidate aspects, one can use dynamic weaving to add or remove them from a system at runtime. The aspect-oriented approach proposed starts with the identification and specification of crosscutting concerns and follows by composing these using modeling aspects using a transformation approach, an aspect-oriented modeling technique. The conflicts that can emerge due to the composition order are also taken into consideration. Finally, this paper proposes a set of reusable GIS crosscutting concerns, documenting them in a concern catalogue.     

On the use of clone detection for identifying crosscutting concern code

In systems developed without aspect-oriented programming, code implementing a crosscutting concern may be spread over many different parts of a system. Identifying such code automatically could be of great help during maintenance of the system. First of all, it allows a developer to more easily find the places in the code that must be changed when the concern changes and, thus, makes such changes less time consuming and less prone to errors. Second, it allows the code to be refactored to an aspect-oriented solution, thereby improving its modularity. In this paper, we evaluate the suitability of clone detection as a technique for the identification of crosscutting concerns. To that end, we manually identify five specific crosscutting concerns in an industrial C system and analyze to what extent clone detection is capable of finding them. We consider our results as a stepping stone toward an automated "aspect miner" based on clone detection.     

基于AOP的面向对象程序的单元测试

单元测试被视为横切关注点,在软件测试过程中很重要。而面向方面编程(AOP)的主要目标就是分离横切关注点,因此,单元测试非常适合用AOP来解决。该文提出了在对面向对象程序进行单元测试时遇到的问题,并用AOP方法加以解决,同时比较了传统方法和AOP方法进行单元测试的优缺点。     

An empirical study of aspect-oriented metrics

Metrics for aspect-oriented software have been proposed and used to investigate the benefits and the disadvantages of crosscutting concerns modularisation. Some of these metrics have not been rigorously defined nor analytically evaluated. Also, there are few empirical data showing typical values of these metrics in aspect-oriented software. In this paper, we provide rigorous definitions, usage guidelines, analytical evaluation, and empirical data from ten open source projects, determining the value of six metrics for aspect-oriented software (lines of code, weighted operations in module, depth of inheritance tree, number of children, crosscutting degree of an aspect, and coupling on advice execution). We discuss how each of these metrics can be used to identify shortcomings in existing aspect-oriented software.     

Guest Editorial: Special Issue on Software Maintenance and Evolution

In systems developed without aspect-oriented programming, code implementing a crosscutting concern may be spread over many different parts of a system. Identifying such code automatically could be of great help during maintenance of the system. First of all, it allows a developer to more easily find the places in the code that must be changed when the concern changes and, thus, makes such changes less time consuming and less prone to errors. Second, it allows the code to be refactored to an aspect-oriented solution, thereby improving its modularity. In this paper, we evaluate the suitability of clone detection as a technique for the identification of crosscutting concerns. To that end, we manually identify five specific crosscutting concerns in an industrial C system and analyze to what extent clone detection is capable of finding them. We consider our results as a stepping stone toward an automated "aspect miner” based on clone detection.     

Aspect-oriented programming will improve quality

Software engineers are always looking for ways to improve modularity in software. Doing so makes software easier to develop and maintain and improves its overall quality. Recently, aspect-oriented programming emerged as a new modularity technique that aims to cleanly separate the implementation of crosscutting concerns (requirements and design elements that affect multiple modules). AOP is an evolutionary step that improves the implementation's comprehensibility and simplifies incorporating new requirements as well as changes to existing ones. This systematic approach promises direct mapping of requirements and design intentions to the implementation. Such a mapping lets you trace the reasoning behind a piece of code's existence. Efficiently implementing crosscutting concerns also has an important indirect benefit: it frees resources to concentrate on the quality of the core implementation. All these factors work together to improve software quality.     

面向方面体系结构建模研究

面向方面体系结构建模是面向方面软件开发(AOSD)的重要组成部分,也是近些年面向方面领域研究的热点问题。传统的软件体系结构设计方法没有单独地考虑横切关注点。因此,在软件体系结构设计阶段,建模人员需要新的机制来描述这些横切关注点。本文首先提出一个以横切为中心的面向方面体系结构概念框架;然后通过在体系结构设计阶段引入该框架中的核心概念,提出一种在体系结构设计阶段建模横切关注点的方法,从而支持其在早期进行横切关注点的分离。     

The real costs of aspect-oriented programming

As a software developer, one of my principal objectives is to deliver the highest quality software possible. Unfortunately, as a human being, my abilities are also my limitations, and I always make mistakes of one kind or another. To remedy this, I use tools to help ameliorate as many of my limitations as possible. One of rny concerns is to understand how using a particular tool affects my ability to meet objectives. How does it help with the various software development tasks? What does it Cost me to use a particular tool? Do the benefits outweigh the costs? If so, what degree is the benefit? If not, then the tool is of little use. There must be a significant benefit gain to justify using a tool. The essence of aspect-oriented programming is that crosscutting concerns are factored into distinct abstractions (that is, aspects) that are solely responsible for a particular crosscutting concern. This raises the system's modularity and increases cohesion of the abstractions that are primary concerns. Researchers and software developers must understand and address the various significant weaknesses before AOP's benefits can be realized.     

AspectLISA: An Aspect-oriented Compiler Construction System Based on Attribute Grammars

The use of object-oriented techniques and concepts, like encapsulation and inheritance, greatly improves language specifications towards better modularity, reusability and extensibility. Additional improvements can be achieved with aspect-oriented techniques since semantic aspects also crosscut many language constructs. Indeed, aspect-oriented constructs have been already added to some language specifications. The LISA compiler construction system follows an object-oriented approach and has already implemented mechanisms for inheritance, modularity and extensibility. Adding aspects to LISA will lead to more reusable language specifications. In the paper, aspect-oriented attribute grammars are introduced, and the underlying ideas are incorporated into AspectLISA, an aspect-oriented compiler generator based on attribute grammars.     

AOP技术在J2EE系统构建中的应用

在应用系统构建中,如何处理系统中的横切关注点问题是系统开发成功的关键。用OO技术来实现这些横切关注点,会导致系统侵入式实现,难于理解和维护。而AOP技术是用来模块化横切关注点的新技术。使用AOP技术来实现横切关注点,使得实现容易设计、理解和维护。而且AOP技术使系统开发高效、高质量,更有能力来实现新的特征。Spring是一个实现控制反转模式(IOC)和面向方面(AOP)的轻量级容器框架,它是用来帮助解决企业应用系统中公共问题和处理企业应用系统开发的复杂性。文中介绍了AOP的基本概念和Spring框架,并举例说明了AOP技术在J2EE系统中应用。     

Tool-Supported Refactoring of Existing Object-Oriented Code into Aspects

Aspect-oriented programming (AOP) provides mechanisms for the separation of crosscutting concerns - functionalities scattered through the system and tangled with the base code. Existing systems are a natural testbed for the AOP approach since they often contain several crosscutting concerns which could not be modularized using traditional programming constructs. This paper presents an automated approach to the problem of migrating systems developed according to the object-oriented programming (OOP) paradigm into aspect-oriented programming (AOP). A simple set of six refactorings has been defined to transform OOP to AOP and has been implemented in the AOP-migrator tool, an Eclipse plug-in. A set of enabling transformations from OOP to OOP complement the initial set of refactorings. The paper presents the results of four case studies, which use the approach to migrate selected crosscutting concerns from medium-sized Java programs (in the range of 10K to 40K lines of code) into equivalent programs in AspectJ. The case study results show the feasibility of the migration and indicate the importance of the enabling transformations as a preprocessing step     

基于 UML扩展的面向方面建模 *

面向方面编程 ( AOP)把横切关注点从系统中分离 ,解决了面向对象编程 ( OOP)中代码纠缠、散射的问题。但在面向方面建模中 ,横切方面没有得到很好的支持。首先 ,在统一建模语言 ( UML)元模型的基础上利用类图建立了整体框架模型 ,设计了核心类、方面、横切元素及其之间的关系 ;其次 ,利用 UML扩展机制为切点、通知、方面等主要元素建立了新的模型 ,设计了它们与方面之间新的关联关系并为其定义了语义。通过 UML扩展,使得 UML能够直接表达面向方面概念 ,支持面向方面建模设计 ,实现了面向方面模型     

A Petri net-based approach for supporting aspect-oriented modeling

The concept of aspect-orientation allows for modularizing crosscutting concerns as aspect modules. Aspect-orientation originally emerged at the programming level, and has stretched over other development phases now. Among them aspect-oriented modeling (AOM) is a hot topic, and there are many approaches supporting it. Petri net is a good formalism which can provide the foundations for modeling software and simulating its execution, but fails to resolve the problem of crosscutting concerns to support AOM. So, this paper presents an approach which extends the Petri net so as to support the AOM. In this paper, the basic functions of the system are modeled as base net by Petri net, and the crosscutting concerns are modeled as aspect nets. In order to analyze the whole system, woven mechanism is proposed to compose the aspect nets and base net together. The problems about aspect-aspect conflict and conflict relations may exist among the aspect nets matching the shared join point, thus this paper propose solutions to resolve them. The Object Petri net which is an extension of traditional Petri net is also extended so as to support aspect-oriented modeling here.     

基于 UML扩展的面向方面建模 *

面向方面编程（AOP）把横切关注点从系统中分离,解决了面向对象编程（OOP）中代码纠缠、散射的问题。但在面向方面建模中,横切方面没有得到很好的支持。首先,在统一建模语言（UML）元模型的基础上利用类图建立了整体框架模型,设计了核心类、方面、横切元素及其之间的关系;其次,利用UML扩展机制为切点、通知、方面等主要元素建立了新的模型,设计了它们与方面之间新的关联关系并为其定义了语义。通过UML扩展,使得UML能够直接表达面向方面概念,支持面向方面建模设计,实现了面向方面模型的可视化和可辨别性;整体框架模型使得面向方面整体结构清晰,各个核心元素之间关系明确,为面向方面建模提供了一个整体设计平台,提高了面向方面软件设计的模块化,增强了代码的重用性和系统的可维护性。     

A Petri net-based approach for supporting aspect-oriented modeling

The concept of aspect-orientation allows for modularizing crosscutting concerns as aspect modules. Aspect-orientation originally emerged at the programming level, and has stretched over other development phases now. Among them aspect-oriented modeling (AOM) is a hot topic, and there are many approaches supporting it. Petri net is a good formalism which can provide the foundations for modeling software and simulating its execution, but fails to resolve the problem of crosscutting concerns to support AOM. So, this paper presents an approach which extends the Petri net so as to support the AOM. In this paper, the basic functions of the system are modeled as base net by Petri net, and the crosscutting concerns are modeled as aspect nets. In order to analyze the whole system, woven mechanism is proposed to compose the aspect nets and base net together. The problems about aspectaspect conflict and conflict relations may exist among the aspect nets matching the shared join point, thus this paper propose solutions to resolve them. The Object Petri net which is an extension of traditional Petri net is also extended so as to support aspect-oriented modeling here.