Modelling techniques for object-oriented design

It is increasingly recognised that an object-oriented approach offers the most promising way forward for the design and production of software systems. In this paper we adopt this point of view, and discuss a problem which arises from it, namely that there is a basic incompatibility between the underlying concepts of object oriented design and the techniques available for modelling software systems in the early stages of development. From the most popular system modelling techniques we select Entity Life Histories as the one which can be made to map most happily onto an object oriented design. We show how this can be achieved and how, by a simple enhancement, Entity Life Histories can be adapted to reflect inheritance and reusability in object-oriented design. The example we use is that of a simple card which is issued for identification purposes and more sophisticated versions which incorporate a PIN number for the user and which may be used to allow access to restricted areas of a building.