Mira Mezini

Conquering aspects with Caesar

Join point interception (JPI), is considered an important cornerstone of aspect-oriented languages. However, we claim that JPI alone does not suffice for a modular structuring of aspects. We propose CAESAR, a model for aspect-oriented programming with a higher-level module concept on top of JPI, which enables reuse and componentization of aspects, allows us to use aspects polymorphically, and introduces a novel concept for dynamic aspect deployment.

Aspect-oriented programming and modular reasoning

Aspects cut new interfaces through the primary decomposition of a system. This implies that in the presence of aspects, the complete interface of a module can only be determined once the complete configuration of modules in the system is known. While this may seem anti-modular, it is an inherent property of crosscutting concerns, and using aspect-oriented programming enables modular reasoning in the presence of such concerns.

Aspect-Oriented Web Service Composition with AO4BPEL

Web services have become a universal technology for integration of distributed and heterogeneous applications over the Internet. Many recent proposals such as the Business Process Modeling Language (BPML) and the Business Process Execution Language for Web Services (BPEL4WS) focus on combining existing web services into more sophisticated web services. However, these standards exhibit some limitations regarding modularity and flexibility. In this paper, we advocate an aspect-oriented approach to web service composition and present AO4BPEL, an aspect-oriented extension to BPEL4WS. With aspects, we capture web service composition in a modular way and the composition becomes more open for dynamic change.

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.

An overview of caesarj

CaesarJ is an aspect-oriented language which unifies aspects, classes and packages in a single powerful construct that helps to solve a set of different problems of both aspect-oriented and component-oriented programming. The paper gradually introduces the concepts of the language and illustrates them by showing how they can be used for noninvasive component refinement and integration, as well as for development of well modularized flexible aspects. In this way we demonstrate that the combination of aspect-oriented constructs for joinpoint interception with advanced modularization techniques like virtual classes and propagating mixin composition can open the path towards large-scale aspect components.

Variability management with feature-oriented programming and aspects

This paper presents an analysis of feature-oriented and aspect-oriented modularization approaches with respect to variability management as needed in the context of system families. This analysis serves two purposes. On the one hand, our analysis of the weaknesses of feature-oriented approaches (FOAs for short) emphasizes the importance of crosscutting modularity as supported by the aspect-oriented concepts of pointcut and advice. On the other hand, by pointing out some of AspectJs weaknesses and by demonstrating how Caesar, a language which combines concepts from both AspectJ and FOAs, is more effective in this context, we also demonstrate the power of appropriate support for layer modules.

Hybrid web service composition: business processes meet business rules

Over the last few years several process-based web service composition languages have erged, such as BPEL4WS and BPML. These languages define the composition on the basis of a process that specifies the control and data flow among the services to be composed. In this approach, the whole business logic underlying the composition including business policies and constraints is coded as a monolithic block. As a result, business rules are hard to change without affecting the core composition logic. In this paper, we propose a hybrid composition approach: The composition logic is broken down into a core part (the process) and several well-modularized business rules that exist and evolve independently. We also discuss two alternative technologies for implenting business rules in encapsulated units, using aspects and a rule-based engine. Our approach allows for a more modular and flexible web service composition.

Virtual machine support for dynamic join points

A widespread implementation approach for the join point mechanism of aspect-oriented languages is to instrument areas in code that match the static part of pointcut designators, inserting dynamic checks for that part of matching that depends on run-time conditions, if needed. For performance reasons, such dynamic checks should be avoided whenever possible. One way to do so is to postpone weaving of advice calls until run-time, when conditions determining the emergence of join points hold. This calls for fluid code---code that adapts itself to the join point emergence at run-time, and suggests that AOP concepts should be integrated into the execution model underlying a VM. In this paper, we present first steps toward such an integration in Steamloom, an extension of IBMs Jikes Research Virtual Machine. Steamloom is fairly restricted, but our initial experimental results indicate that aspect-aware VMs and fluid code are promising w.r.t performance. While the focus in this paper is on performance, there are other advantages of aspect-aware VMs to be investigated in the future.

Expressive pointcuts for increased modularity

In aspect-oriented programming, pointcuts are used to describe crosscutting structure. Pointcuts that abstract over irrelevant implementation details are clearly desired to better support maintainability and modular reasoning. We present an analysis which shows that current pointcut languages support localization of crosscutting concerns but are problematic with respect to information hiding. To cope with the problem, we present a pointcut language that exploits information from different models of program semantics, such as the execution trace, the syntax tree, the heap, static type system, etc., and supports abstraction mechanisms analogous to functional abstraction. We show how this raises the abstraction level and modularity of pointcuts and present first steps toward an efficient implementation by means of a static analysis technique.

Taming reflection: Aiding static analysis in the presence of reflection and custom class loaders

Static program analyses and transformations for Java face many problems when analyzing programs that use reflection or custom class loaders: How can a static analysis know which reflective calls the program will execute? How can it get hold of classes that the program loads from remote locations or even generates on the fly? And if the analysis transforms classes, how can these classes be re-inserted into a program that uses custom class loaders? In this paper, we present TamiFlex, a tool chain that offers a partial but often effective solution to these problems. With TamiFlex, programmers can use existing static-analysis tools to produce results that are sound at least with respect to a set of recorded program runs. TamiFlex inserts runtime checks into the program that warn the user in case the program executes reflective calls that the analysis did not take into account. TamiFlex further allows programmers to re-insert offline-transformed classes into a program. We evaluate TamiFlex in two scenarios: benchmarking with the DaCapo benchmark suite and analysing large-scale interactive applications. For the latter, TamiFlex significantly improves code coverage of the static analyses, while for the former our approach even appears complete: the inserted runtime checks issue no warning. Hence, for the first time, TamiFlex enables sound static whole-program analyses on DaCapo. During this process, TamiFlex usually incurs less than 10% runtime overhead.