Separation of concerns and modularization are the cornerstones of software engineering. However, when a system is decomposed into units, functionalities often emerge which cannot be assigned to a single element of the decomposition. The implementation of interfaces¹ represents a typical instance of this problem. In fact, the code that defines the interface methods is often scattered across several classes in the system and tangled with the original code.

Aspect Oriented Programming provides mechanisms for the dynamic and static composition of transversal functionalities, that can be used to factor out the implementation of interfaces. In this paper we describe a technique for the identification of those interface implementations that are most likely to represent crosscutting concerns. Moreover, the code transformation (refactoring) to migrate such interfaces to aspects is also presented. Experimental results validate the approach.