When trying to describe the behaviour of large systems, such as the business processes of large enterprises, we often adopt diagramming techniques based on derivatives of data flow diagrams. For very complex systems such diagramming techniques suffer from the inability to abstract uniformly from arbitrary subcollections of components. We present an extension to conventional diagramming techniques which solves this problem. We describe how we have applied this technique to some very complex business systems and illustrate its main points with a simple example. While we have used the notation to present models of business processes we conclude that it is applicable to the description of behaviour in any complex system of processes.