Towards a Generic Framework for AOP

Abstract

During the 1st workshop on AOP [AOP97] several fundamental questions were raised: What exactly are aspects? How to weave? What are the join points used to anchor aspects into the component program? Is there a general purpose aspect language? In this position paper, we address these questions for a particular class of aspects: aspects expressible as static, source-to-source program transformations. An aspect is defined as a collection of program transformations acting on the abstract syntax tree of the component program.We discuss the design of a generic framework to express these transformations as well as a generic weaver. The coupling of component and aspect definitions can be defined formally using operators matching subtrees of the component program. The aspect weaver is simply a fixpoint operator taking as parameters the component program and a set of program transformations. In many cases, program transformations based solely on syntactic criteria are not satisfactory and one would like to be able to use semantic criteria in aspect definitions. We show how this can be done using properties expressed on the semantics of the component program and implemented using static analysis techniques. One of our main concerns is to keep weaving predictable. This raises several questions about the semantics (termination, convergence) of weaving.