Modelling business processes in general is a complex endeavour, as many different aspects such as the control flow, the management of data, event and message handling, actors and interaction, exception handling, etc. have to be taken into account, all of which require different models. This paper focuses on the horizontal integration of models for control flow, message flow, event handling, interaction, actors, data handling and exception handling. The method is based on Abstract State Machines (ASMs), which are used to formally define the semantics of each of the individual models. Throughout the process rigorous quality assurance methods will be applied.