Using the Function Hierarchy and Function Dynamics models, you determine the items of data that you intend to process in your application. To start with, the groups of data items that comprise entities are identified.
For example, a name, address and balance of account are all items of data that relate to a customer. These data items can be grouped into an entity called CUSTOMER. The example Sales Order system has the entities CUSTOMER, MATERIAL, ORDER_HEADER and ORDER_LINE.
You need to show the relationships between identities on the diagram, for example:
A customer places many orders.
An order consists of many order lines.
A material is specified in many order lines
The relationships between the tables in the Sales Order database are shown in the next diagram:
In our convention, the split lines or 'crows' feet' at the end of the lines on the diagram indicate the one-to-many relationships between the entities.