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Diagramming Data Objects

Now you know and understand the entities and relationships in your database, which is the most important part of the relational-database design process. After you determine the entities and relationships, a method that displays your thought process during database design might be helpful.

Most data-modeling methods provide some way to graphically display the entities and relationships. IBM Informix documentation uses the E-R diagram approach that C. R. Bachman originally developed. E-R diagrams serve the following purposes. They:

Several different styles of E-R diagrams exist. If you already have a style that you prefer, use it. Figure 12 shows a sample E-R diagram.

Figure 12. Symbols of an Entity-Relationship Diagram
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In an E-R diagram, a box represents an entity. A line represents the relationships that connect the entities. In addition, Figure 13 shows how you use graphical items to display the following features of relationships:

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