\begin{abstract}

Inter-type declarations (ITDs) in current aspect-oriented languages have
limited extensibility: it is difficult to change the behavior of
existing ITDs when extending a system written in an aspect-oriented
language. We introduce a module system that allows for ITD extensibility 
through module subtyping, and demonstrate that modules also provide 
the additional benefits of information hiding and explicit dependency 
specification. The module system is also used on a moderately-sized 
case study on a Java compiler written in JastAdd, an aspect-oriented 
compiler construction framework.

\end{abstract}
