Models and modelling
Models and modelling

Start this free course now. Just create an account and sign in. Enrol and complete the course for a free statement of participation or digital badge if available.

8 Entity–relationship data modelling

8.1 Introduction

One type of data model is an entity–relationship data model.

Experience has shown that data can be best described by relationships between entities. An entity is anything of interest about which data is recorded, such as roads, weather stations, trucks and weather station readings in the IceBreaker project in the book MRP. In general, there will be many relationships (or associations) linking the entities. A trivial example is the fact that a given weather reading is associated with a specific weather station. The significant point is that relationships are just as much a part of the system data as are the entities. It is often useful to store characteristics of the entities. For example, a particular type of weather station transmits its signal every minute, or a specific truck has a particular capacity for the amount of gritting material it can carry.

Many different kinds of relationship between entities have been identified, and there are many different ways of representing those relationships. Diagrams are often used to show relationships, but there are other techniques.

Data modelling, that is, the production of a data model is a ‘formal’ representation of what data the product needs, expressed in terms that are independent of how it may be realised in software. Entity–relationship (E–R) data modelling is a particular kind of modelling that expresses data requirements in terms of entity types, attributes of entity types and relationships between entity types. It is a widely used modelling technique which is effective for displaying the important elements of a data model for human understanding and communication. However, it is only one of a number of modelling techniques available. We shall use an example to illustrate E–R data modelling.

Take your learning further

Making the decision to study can be a big step, which is why you'll want a trusted University. The Open University has 50 years’ experience delivering flexible learning and 170,000 students are studying with us right now. Take a look at all Open University courses.

If you are new to University-level study, we offer two introductory routes to our qualifications. You could either choose to start with an Access module, or a module which allows you to count your previous learning towards an Open University qualification. Read our guide on Where to take your learning next for more information.

Not ready for formal University study? Then browse over 1000 free courses on OpenLearn and sign up to our newsletter to hear about new free courses as they are released.

Every year, thousands of students decide to study with The Open University. With over 120 qualifications, we’ve got the right course for you.

Request an Open University prospectus371