An Express model for the description of fieldbus devices

The paper deals with the definition of a device description model which takes into account the most significant features of the fieldbus devices currently available on the market and included in the EN50170 European standard. The basic concepts that can be found in the relevant international standards have been taken as a basis for the development of the model. The model is formally described in Express since it is a well assessed data modeling language for which a graphical subset also exists. Several tools for processing Express models are widely available nowadays on different platforms. Hence, the model can be translated into a corresponding representation for a specific host language with relatively little effort. The basic aim is that of providing a common understanding of the device features through the structured organization of data, parameters, event and actions so that interoperability is guaranteed independently of the specific fieldbus technology used in the network. Each device is described using the entity relationship approach and takes advantage of the inheritance property which leads to a simple and immediate description of new device features which can be added to the hierarchy without affecting the existing structure of the model. As an example, the paper also shows how the proposed general model can be refined to describe a particular class of real devices including more specific attributes and events.