Interoperability seems to be a major focal point of the activities within the Informatics Society in general, and the Medical Informatics society in particular. In both Europe and the USA standardization efforts are pursued in order to enable interoperability. However, even if the technical requirements are met, interoperability is sometimes not feasible because the message exchange needed is too complex. This complexity is influenced by at least three factors: the volume of the data to be exchanged, the functionality of the information exchange, and the communication standard adopted.