Frameworks are increasingly being recognised as very useful components in the emerging paradigm of component-based software development (CBD). They are widely accepted as better units of reuse than objects. The CBD methodology Catalysis, for instance, uses frameworks. However, at present, Catalysis frameworks are described only informally, which means we cannot reason formally about frameworks, in particular their composition, and thereby their reuse. For this, we would need to specify frameworks (and their composition) formally. In this paper, we describe our approach for doing so.