From Aspect - Oriented Model to Implementation Watch Out for Impedance Mismatch

An important part of both comprehensibility and traceability is that the implementation resemble the design. As the design is refined to a concrete implementation, it is important that concepts have a clear correspondence to implementation artifacts – even if this mapping is not one-to-one. This holds true for crosscutting – or aspect-oriented – behaviors as well. We illustrate by investigating the Observer pattern, modeled using subject-oriented extensions to UML, and implemented in AspectJ. We identify three properties that don’t match between design and implementation, and conclude that all are due to impedance mismatch between the abstract design and the concrete language.