Controlling the Complexity of Software Designs

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Controlling the Complexity of Software Designs
pp. 2 11

• Karl J. Lieberherr
• 26th International Conference on Software
  Engineering (2004)

Poster by John Volk
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Aspect Oriented Programming

• Attempts to isolate concerns that cross-cut an
  entire application into abstractions called
  aspects.
• For each aspect that a developer wants to
  encapsulate, he or she must define the join
  points at which this code needs to be executed,
  and the block of code itself.

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Law of Demeter (LoD)

• Talk only to your friends.
• Only allowed to send messages to objects supplied
  in the arguments to a method (including this), or
  objects created in the method.
• Simplifies code by minimizing the number of
  modules to which a single module can refer.

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Law of Demeter for Concerns

• Stricter form of LoD.
• Has the same restrictions as LoD, but adds one
• Modules are not permitted to send messages to
  other modules if those modules do not contribute
  to the current concern.
• Concern Any issue that the designer/programmer
  is concerned with, e.g., the synchronization
  policy of a system, the implementation of a use
  case, or the exception handling policy of a
  system.

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Example Logging

• You want to add logging for important events to
  an existing software system.
• First Option
• Decide which events needs to be logged, find the
  code where those events occur, add calls to some
  logging component in the necessary places.
• Problems with this approach
• You have to change code in a lot of places.
• Violates the LoDC. Code for one concern is
  sending messages to code dealing with a different
  concern.

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Example Logging (contd.)

• Second Option
• Define the logging code as an aspect.
• Define join points from where the logging aspect
  needs to be called.
• Benefits
• You dont have to change any old code.
• Its very easy to plug the logging code in and
  out of your application. Just add/remove the
  aspect.

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AOP Tools

• AspectJ allows a developer to define aspects and
  join points to use in concert with existing Java
  code.
• Example
• aspect Logging
• pointcut find_Cwithdraw()
• call( C.withdraw(..))
• after find_Cwithdraw()
• System.out.println(thisJoinPoint)

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Critique

• One main problem
• Lack of concrete examples. Most of the
  information one can find on AOP immediately
  points to the logging example. This paper was no
  different.
• If researchers in AOP want to have professional
  Software Engineers begin to use the technology,
  there probably going to have to come up with more
  concrete scenarios where AOP can be used for
  significant improvements in the development
  process.

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Questions

• What is Aspect Oriented Programming?
• What is an example commonly used to explain the
  benefits of Aspect Oriented Programming?
• What is one benefit of Aspect Oriented
  Programming?