On the Assessment of Pointcut Design in Evolving Aspect-Oriented Software

The pointcut expression (PCE) is a key mechanism in enabling Aspect-Oriented Programming (AOP) (Kiczales et al. 1997) to improve the localization of crosscutting concerns. PCEs quantify over well-defined points in the execution of the program called join points. A join point shadow, on the other hand, refers to base-code corresponding to a join point (Xu and Rountev 2008), i.e., a point in the code where the compiler may perform the weaving (Masuhara et al. 2003). Advice joins at these points to allow the crosscutting concerns to be composed in an appropriate manner. PCEs need to be well-designed to ensure that they are correct in terms of identifying relevant join points to make certain the crosscutting concerns are composed correctly. Furthermore, PCEs should be robust in the midsts of base-code alterations. That is, changes to the base-code can lead to join points incorrectly falling in our out of scope of the pointcut expressions. Such situations are problematic in that they can cause crosscutting concerns to be composed incorrectly. If undetected, this could cause the composed program to behave unexpectedly, thus causing errors to occur. PCEs that result in such unexpected behavior of the composed program due to evolution are often referred to as “fragile” (Koppen and Stoerzer 2004). The skill required to design a robust PCE, especially in languages such as AspectJ (Kiczales et al. 2001), is often considered a “dark-art”, as well as associated with many common pitfalls (Colyer et al. 2004). Typically, a number of alternative PCEs exist that are equivalent in terms of their