For the development of a rheumatology information system, a medical data dictionary was developed that supports all phases of software development. In the design phase, the medical expert described his clinical environment and the rheumatology medical record in a semantic network structure. Causal relationships between different items of the medical record (e.g., a problem may be related to an adverse drug event caused by a particular drug) are also represented in the semantic network and transferred into referential integrity constraints of the patient database. Furthermore, by also integrating the domain management as a feature of the medical data dictionary, the elementary attributes of the medical record and the associated lists of valid attribute entries have also been defined within the semantic network. This structure allowed the automatic generation of data entry screens, thus making the clinical applications as independent from any hardcoded program module as possible.