Making aspects natural: events and composition

Language extensions are proposed to make aspects more natural for programmers. The extensions involve two main elements: (1) Completely separating the identification of events and locally accumulating information about them from any possible response to the events, and (2) composing both events and aspects into hierarchies that loosen the connection to code-level methods and field names. The combination of these extensions are shown (in preliminary experiments) to increase modularity, and facilitate using terminology natural for each concern. Extensions to AspectJ and Compose* are shown to illustrate how the concepts can be easily embodied in particular languages. The execution model of ALIA4J is used to present the concepts in a language-independent way, providing a prototype generic implementation of the extensions, that can be used to implement them for both AspectJ and Compose*. The extensions increase the flexibility of aspects, encourage reuse, and allow expressing events and responses to them in terms natural to the concern that an aspect treats.