ASPECT ORIENTED SOFTWARE DEVELOPMENT Prepared By: Ebru Doğan

Presentation Outline 1. Current Methods and Languages 2. Separation of Concerns (SOC) 3. Problem: cross-cutting 4. Concepts of Aspect-Oriented Development 5. Aspect Oriented Programming (AOP) 6. Applications: Tracer example 7. Integration Aspects and Components 8. Conclusions 9. 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 Paradigms ParadigmAbstractionModularization Structured programming control flowcontrol structure Procedural programming computationsprocedure Object-oriented programming data typesclass/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 AOP 1. 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 oriented_programming [Fil05] “Aspect-Oriented Software Development” by R.Filman et al., ISBN: