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Entity Relationship Diagrams (ER)

Now that we have the DFDs, we have the system view of the main functions and processes in the new system. Another important stage in the development is creating Entity Relationship diagrams, which will help us understand the data model view of the system.

Data modelling is a technique that is widely used in the world of business and information technology to show how information is, or should be, stored and used within a system. The success of any organisation relies on the efficient flow and processing of information.

Let's look at an example in which information flows around the various departments in the organisation. This information can take many forms; for example it could be written, oral or electronic.

Example of Entity Relationship Diagram

The General Manager regularly communicates with staff in the sales and marketing and accounts departments by using email. Orders received by sales and marketing are forwarded to the production and accounts departments for completion and invoicing. The accounts department forwards regular written reports to the General Manager. It also raises invoices and sends these to the customers.

Data modelling is a technique aimed at making the most of the way that information is stored and used in an organisation. It begins with the identification of the main data groups, for example the invoice, and continues by defining the detailed content of each of these groups. This results in structured definitions for all of the information that is stored and used within a system.

The technique provides a solid foundation for systems design and a universal standard for system documentation. Data modelling is an essential precursor to analysis and design, maintenance and documentation, and improving the performance of an existing system.

Next: Data Modelling Symbols