Softening Dependencies between Interfaces

An object-oriented application programming interface (API) must satisfy two con icting requirements. On the one hand, it is desirable to have a low-level, primitive API, in order to simplify documentation and speci cation of semantics, and to make the API accessible to a large group of potential developers. On the other hand, a particular application programmer often requires higher level access and search methods to accomplish common combined operations. This often results in \bloating" of the API with high-level operations, whenever enough users (i.e., applications programmers) are found to require them. In this paper we present a solution to this dilemma which allows for convenient customized extension of a basic, object-oriented API. The extension technique uses traversal strategies to succinctly de ne the composition of high level methods out of low level methods. This technique has several advantages over direct customization using a general purpose programming language; the extension is more robust to changes in the base API, and the process is more systematic and less error prone. In this paper we present a system called Persephone that implements this extension technique. We demonstrate its use by exhibiting a customized extension to the API for a complex architecture interchange language.