Rejuvenate Pointcut: A Tool for Pointcut Expression Recovery in EvolvingAspect-Oriented Software∗

Raffi T. Khatchadourian†

Ohio State Universitykhatchad@cse.ohio-state.edu

Awais RashidLancaster University

awais@comp.lancs.ac.uk

Abstract

Aspect-Oriented Programming (AOP) strives to localizethe scattered and tangled implementations of crosscuttingconcerns (CCCs) by allowing developers to declare thatcertain actions (advice) should be taken at specific points(join points) during the execution of software where a CCC(an aspect) is applicable. However, it is non-trivial toconstruct optimal pointcut expressions (a collection of joinpoints) that capture the true intentions of the programmerand, upon evolution, maintain these intentions. We demon-strate an AspectJ source-level inferencing tool called REJU-VENATE POINTCUT which helps developers maintain point-cut expressions over the lifetime of a software product. Akey insight into the tool’s construction is that the problemof maintaining pointcut expressions bears strong similarityto the requirements traceability problem in software engi-neering; hence, the underlying algorithm was devised byadapting existing approaches for requirements traceabil-ity to pointcut maintenance. The Eclipse IDE-based toolidentifies intention graph patterns pertaining to a pointcutand, based on these patterns, uncovers other potential joinpoints that may fall within the scope of the pointcut witha given confidence. This work represents a significant steptowards providing tool-supported maintainability for evolv-ing aspect-oriented software.

1 IntroductionAspect-Oriented Programming (AOP) has emerged to lo-

calize the scattered and tangled implementations of cross-cutting concerns (CCCs) in source code, allowing develop-ers to characterize that certain actions (advice) should betaken at specific points (join points) during the executionof software. The applicability of advice is denoted via theuse of a pointcut expression (PCE) which specifies where aCCC (an aspect) is applicable. A PCE does so by logically

∗This material is based upon work supported by the European Commission grantIST-33710 (AMPLE) and grant IST-2-004349 (AOSD-Europe).

†This work was administered during this author’s visit to the Computing Depart-ment, Lancaster University, United Kingdom.

connecting various predicate expressions over static and dy-namic program characteristics like method and field namingconventions, lexical scope, and execution control-flow.

The true power of AOP lies not only in the ability to ex-press the applicability of existing join points captured bya PCE but also in the applicability of join points that willbe added in the future. An effective PCE is one that trulyconveys the essence of where a CCC applies in the under-lying system (base-code) so that not only are the currentjoin points that correspond to where a CCC applies are se-lected but future ones as well. Thus, creating effective PCEsrequires developers to anticipate structural (static) and be-havioral (dynamic) properties that the base-code will ex-hibit as the software evolves. Constructing such optimalPCEs, however, can be a daunting task, especially consid-ering that these expressions should remain valid as the soft-ware evolves. The problem is that as new requirements sur-face and corresponding program elements emerge to real-ize a particular requirement, the PCEs which were once in-tended to capture core (base) concerns in which a certainCCC was deemed applicable may no longer be valid.

It has been shown that the cause of this problem isrooted at the inherent fragility of the typical PCE languageavailable in popular AO languages such as AspectJ For-tunately, maintaining PCEs as software evolves seems toshare some resemblances to the requirements traceabilityproblem. Software is said to be requirement traceable if adeveloper has the ability to follow the life of the realizationof a particular requirement in both a forwards and back-wards direction. Unfortunately, the luxury of possessingsuch an ability can necessitate a significant amount of costlydeveloper time; therefore, it is essential to cache such infor-mation for later consultation. Nevertheless, even seeminglyinnocuous changes to any traced element are likely to inval-idate the corresponding trace information. Consequently,effort must be made to maintain the trace information witheach artifact alteration. This situation is similar to one thatoccurs in AOP, specifically, that PCEs should also be main-tained in a analogous fashion as the base-code evolves.

In an effort to combat this problem, we demonstrate an

Eighth IEEE International Working Conference on Source Code Analysis and Manipulation

978-0-7695-3353-7/08 $25.00 © 2008 IEEE

DOI 10.1109/SCAM.2008.32

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Analyze Patterns

Create advice/modify bound PCE

Associate PointcutDerive Patterns

Analyze Base

Apply Patterns

Abstractnessα

Error

Confidence

Calculate Pattern Confidence

Calculate Wildcard Ratio

Persist Patterns with Confidence

Calculate Pattern Statistics

β Error

Figure 1. Phase I: Pointcut analysis.

AspectJ source-level, inferencing tool named REJUVENATE

POINTCUT. The Eclipse IDE plug-in alleviates the burdenassociated with maintaining PCEs over the lifetime of soft-ware by enabling tool-assisted augmentation of a PCE uponchanges to the base-code. In the following sections, we pro-vide a brief overview of our tool, including a high-level ar-chitecture, and summarize its innovative features.

2 Rejuvenation ApproachTo assist developers maintain PCEs over the lifetime of

the base-code, our tool is composed of two phases: analysisand rejuvenation.

Phase I: Analysis. The analysis phase, whose flow dia-gram is depicted in Figure 1, is triggered upon modificationsto advice-bound pointcuts. The phase consists of analyzingunderlying patterns in the base-code prior to its modifica-tion and then associating the pointcut with these patterns.At the core of Phase I is an interprocedural inferencing algo-rithm that uses an intention graph to capture the developer’sintentions in creating certain program elements. The graphis constructed with the aid of the JayFX fact extractor whichgenerates facts using class hierarchal analysis (CHA) per-taining to structural properties and relationships, e.g., fieldaccesses, method calls, residing in the base-code. The phasethen proceeds to associate the PCE with both vertices andlabeled arcs by leveraging the AspectJ Development Tools(AJDT). These associated graph elements are referred to asenabled with respect to a PCE. Next, intention patterns ex-pressing general shapes of acyclic paths that include en-abled elements are derived. The patterns are then them-selves analyzed in order to produce and associate a confi-dence. This metric symbolizes the degree of credence inusing the pattern to identify join points that should be aug-mented to a given PCE upon base-code evolution. Conse-quently, results produced by the pattern are correlated withand ranked by this confidence when presented to the devel-oper. Finally, the patterns are associated with the PCE and

Rejuvenation Request

Retrieve Prior Patterns Analyze New Base

Apply PatternSuggest Join

PointPattern

Available? Yes

Previously Analyzed PCE

Sort By Confidence

Intention Graph

Incorporate Join Point

Accept?

Match Available?

Yes

Commit PCE Changes

No

No

Yes

No

Initialize

Rejuvenate

Figure 2. Phase II: Pointcut rejuvenation.

persisted for later use in Phase II.Phase II: Rejuvenation. We envision our tool to be

most helpful in scenarios where a developer changes thebase-code and then proceeds to update PCEs to reflect thosechanges so that new join points are captured correctly. Asdepicted in Figure 2, prior to manually altering the PCE, thedeveloper selects the PCE in the Eclipse IDE and executesour tool for assistance in performing the updates correctly.At this juncture, the intention patterns previously associ-ated with the PCE are retrieved from storage and ran againstthe new base-code version in order to unveil the suggestedjoin points, which are those that share intentional similari-ties with the join points previously selected by the PCE inthe original version of the base-code. Each suggestion ispresented with the derived patterns’ confidence. The devel-oper then selects the desired join points to be incorporatedinto a new version of the PCE.

3 Conclusion and Future WorkBy adapting existing approaches for requirement trace-

ability maintenance, the REJUVENATE POINTCUT EclipseIDE plug-in helps developers maintain pointcut expressionsin evolving aspect-oriented software. Additional join pointswhose associated program elements exhibit common pat-terns in the intentional structure of the base-code are sug-gested for incorporation to existing PCEs. In its currentstate, the tool presents the user with the new suggested joinpoints for manual integration. In future versions of the tool,once the selection is final, the pointcut will be rewritten us-ing existing refactoring support adapted for AspectJ con-structs. Furthermore, our current refactoring module proto-type is able to handle simple augmentations, e.g., via dis-junction of join points, however, we plan to utilize existingrefactoring tool-support in order to perform more complexpointcut rewriting via join point clustering and string anal-ysis of program element names.

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