Towards a Composition Taxonomy

Different similarities and differences between AspectJ, the first general-purpose AOP-language, and Hyper/J, a recent implementation of multi-dimensional programming, have been identified. This paper explores how both proposals give different answers to the same question: How can we modify existing classes, that are used by existing clients? In this chapter, different criteria are developed by which all reviewed pro-posals can be compared and classified on an abstract level. Our general model in this chapter is that we have composition units which have to be composed in order to build a composite unit. A composition unit can be almost anything, e. g. objects, classes, mixins, aspects, connectors. In order to compare the new composition models to the existing ones, in-heritance and object composition are included in our investigations. Other well-known language features such as structural subtyping or generic classes are mentioned in case they help to explain a term.