2 Developing the conceptual model
2.1 Main activities in developing a conceptual model
In this section you will learn about:
the activities involved in developing a conceptual model;
the role and purpose of the conceptual model;
the position of the conceptual model in the wider context of the system that is being developed.
The process of constructing a conceptual model starts with an analysis of the requirements document, to identify those entities which are of key significance to the system, excluding any that are irrelevant or peripheral to its core functionality. In the case of the Hospital System, for example, key entities will include things such as patients and wards.
One category of entity that will be excluded at this stage is that which deals with details of input and output – the way in which information will be provided by and to human users of the systems. It is standard practice to separate the development of the user interface from that of the core system, and keep the two as independent of one another as possible. This is because it is quite likely that the user interface will need to be changed after the software has been delivered, for example to accommodate additional types of user or to take advantage of improved technology. This will be much easier to do if the user interface can be altered without requiring changes to the core system. Conversely, changes to the implementation of the core system should be possible while still keeping the user interface the same.
Having identified entities that are of key significance to the system, we need to identify their properties and the various relationships between them. For example, patients are likely to have properties such as their name and age, and to be related to wards by virtue of the fact that each patient is on a particular ward.
It is also necessary to identify constraints on the system domain (i.e. limitations on the entities, their properties and relationships) and decide what conditions such constraints will impose on the model.
The completed conceptual model will consist of a diagram representing the system domain, together with text describing important features of the model.
In summary, the process which takes you from the requirements document to the conceptual model involves the following activities.
Identification of those real-world entities described in the requirements document which are concerned with the core functionality of the system, leaving out considerations of the user interface. These will become the conceptual classes in the model.
Identification of the properties of the entities and the relationships between the entities.
Identification of the conditions that will be imposed on the model.
Representation of the model using diagrams and associated text.