An efficient method of interfacing between patient related data and the signal processing methods used to interpret these data is a critical component for a successful patient monitor, particularly for use in high dependency environments. This paper describes the approach adopted in the IBIS project. The key elements of the system are first introduced. A multi-layer structure is then developed in which the outputs from one decision layer are used to enhance the information available for subsequent layers in the system. The resulting system is modular, robust, flexible and easy to modify.