ASPECT ORIENTEDSOFTWARE

DEVELOPMENT

Prepared By: Ebru Doğan

Presentation Outline

1. Current Methods and Languages2. Separation of Concerns (SOC)3. Problem: cross-cutting4. Concepts of Aspect-Oriented Development5. Aspect Oriented Programming (AOP)6. Applications: Tracer example7. Integration Aspects and Components8. Conclusions9. References

Current Methods and Languages Support abstraction mechanisms for breaking

a system down into components Concentrate on finding and composing

functional units

Benefits of Good Modularity

Also known as “clean separation of concerns”

no scattered code no tangling highly cohesive & loosely coupled

Separation of Concerns - Cohesion Cohesive component performs only one

concern/task

Separation of Concerns - Coupling Two components are independent if they do not

have interactions Highly coupled components have many

dependencies/interactions

Modularity is not always possible...

Some concerns don’t localize to objects

… their code tends to be orthogonal to the rest of the requirements

… and is spread out through many modules

Examples of crosscutting concerns

Synchronization Real-time constraints Error-checking Object interaction constraints Memory management Persistency Security Caching Logging Monitoring Testing Domain specific optimization ...

Example - Figure Editor - Design

Figure Editor Example –cont’d

Crosscutting Concern - Example

Aspect-oriented development Aspect-oriented development addresses separation

of concerns (SOC) Concerns are associated with cross-cutting Cross-cutting concerns are implemented as aspects

and are dynamically woven into a program

Motivation for Aspect-Oriented Programming Programming paradigm for encapsulating

crosscutting concerns into aspects. AOP builds on top of other programming paradigms:

object-oriented, procedural or functional. It does not supplant them.

Key Abstractions for Different Programming ParadigmsParadigm Abstraction Modularization

Structured programming

control flow control structure

Procedural programming

computations procedure

Object-oriented programming

data types class/object

Aspect-Oriented programming

crosscutting concerns

aspect

Concepts of AOP (I)

Aspect: unit encapsulating a crosscutting concern. Join point: point in the execution of a program

where an aspect might intervene. “[...] whenever condition C arises, perform action A”

Pointcut:expression of a subset of join points (condition C) Advice: piece of code for action A. Pointcuts and advice encapsulated into aspects.

Concepts of AOP (II)

Weaving

Few Examples of Existing AOP technologies

AspectJ HyperJ AspectC++ Aspect# Caesar CompositionFilters AspectWerkz JBoss-AOP

Most Popular AOP technology AspectJ

a general purpose AO programming language just as Java is a general-purpose OO language extension to Java

AspectJ

Five simple steps to create an AOP1. Define the core/base functionality classes

2. Define the aspect class

3. Define the pointcut

4. Declare the advice

5. Weave & Compile

Tracer Example – Without AOP

Tracer Example – With AOP

Advantages of AOP

Improves performance Allows better code reuse Enables better code encapsulation

Componentizing Aspects

Representing each aspect as a single reusable component

Map the characteristics of a component on aspect

Explore the applicability of concepts on aspect

Conclusions

Crosscutting concerns are typically scattered over several modules and result in tangled code.

This reduces the modularity and as such the quality of the software system.

AOSD provides explicit abstractions mechanisms to represent these so-called aspects and compose these into programs.

Increases the modularity of systems.

References

http://www.aosd.net/ http://www.eclipse.org/aspectj/ http://en.wikipedia.org/wiki/Aspect-

oriented_programming http://csl.ensm-douai.fr/fakih/phd [Fil05] “Aspect-Oriented Software

Development” by R.Filman et al., ISBN: 0321219767