Transcript (I) Aspect - METU Computer Engineering

ASPECT ORIENTED
SOFTWARE
DEVELOPMENT
Prepared By: Ebru Doğan
Presentation Outline
1.
2.
3.
4.
5.
6.
7.
8.
9.
Current Methods and Languages
Separation of Concerns (SOC)
Problem: cross-cutting
Concepts of Aspect-Oriented Development
Aspect Oriented Programming (AOP)
Applications: Tracer example
Integration Aspects and Components
Conclusions
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
Paradigm
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 AOP
1.
2.
3.
4.
5.
Define the core/base functionality classes
Define the aspect class
Define the pointcut
Declare the advice
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/Aspectoriented_programming
http://csl.ensm-douai.fr/fakih/phd
[Fil05] “Aspect-Oriented Software
Development” by R.Filman et al., ISBN:
0321219767