The 4 Layer Model is a software architecture split up in four layers: User Interface, Application Layer, Domain Layer and the Infrastructure Layer.
Business Domain Engineering which provides generic technical capabilities to the other layers (e.g. persistency, search platform etc.)
User Interface, which is responsible for displaying and entering information. The system has been designed for direct data capture by human users (e.g. clinician and administration). It is extensible for the direct data capture from medical devices (e.g. vital parameter monitors) and diagnostic apparatus (e.g. ultrasonography), and for steering of such devices.
Application Layer, which coordinates tasks among the data objects of the domain layer and the interacting actors (e.g. other applications or human users). This layer is kept thin and does not contain any domain knowledge.
Domain Layer, which represents the domain knowledge by specifying data objects and business rules. The current system mainly uses an abstract tree object, which is dynamically specified by the domain expert through the spreadsheet template.