State-Based Join-Points: Motivation and Requirements

In developing a real-world complex application, we experience the major problem that complex concerns do not easily map onto low-level aspects with join-points based on fixed points in the program code. It is our observation that modularizing concerns and quantification are to be tackled at design-time, using suitable abstractions, with a translation to dynamic weaving at run-time. In particular, we argue that ‘abstract states’ of software entities (a concern consists of software entities) are a promising instrument for defining higher-level join-points for concerns. The specification and quantification of concerns in terms of abstract states typically result in dynamic weaving, i.e. depending on run-time states of the software entities. Based on experience, we provide requirements for supporting concern modelling and quantification at design-time, as well as an initial sketch of an approach that we investigate in this perspective. The approach is based on a new type of higher-level join-points, called state-based join-points and serves as an example of the necessity for advanced dynamic (state-based) aspect weaving. The approach is motivated and illustrated through a scenario in a real-world application, namely decentralized control software for several automatic guided vehicles in an industrial transportation system.