Interacting Frameworks in Catalysis Kung-Kiu Lau Dept of Computer Science University of Manchester Manchester M13 9PL, UK kung-kiu@cs.man.ac.uk Shaoying Liu Dept. of Computer Science Hiroshima City University 151-5, Ozuka, Numata-cho,Asaminami-ku Hiroshima, 731-31, Japan liu@white.sel.cs.hiroshima-cu.ac.jp Mario Ornaghi DSI, Universita' degli studi di Milano Via Comelico 39/41, 20135 Milano, Italy ornaghi@dsi.unimi.it Alan Wills Trireme International Ltd 24 Windsor Road, Manchester M19 2EB, UK alan@trireme.com Abstract: In current OO Design, most of the existing (semi-formal) methods use classes or objects as the basic unit of design. However, it is increasingly recognised that classes are not the best focus for design. Typical design artefacts are about groups of objects and the way they interact. In the Catalysis project, we use the term frameworks for descriptions of groups of objects, their relationships, division of responsibilities, and interactions. The power of frameworks lies in the fact that interactions can also occur at the level of frameworks. In a previous paper, we defined a framework formally as a (first-order) many-sorted theory with a model-theoretic semantics and showed how it can be represented using a pictorial notation for practical system development. However, we considered only frameworks that do not interact with one another. In this paper, we discuss frameworks that interact with one another, and show that such frameworks are very powerful tools for formal OO Design.