An entity relationship diagram (ERD) is the graphical representation of all data stored in a system and their relationships. Another way to put it is the picture of how the information a system produces is connected. There are three main pieces to a ERD:

• Entities, which are represented by rectangles
• Relationships, which are represented by diamond shapes
• Connecting lines, sold lines that connect an entity to a relationship.

An ERD looks very much like a Flowchart.

Typical Uses

When documenting a system or process, looking at the system in multiple ways increases the understanding of that system. ERD diagrams are commonly used in conjunction with a data flow diagram to display the contents of a datastore. They are very helpful when needing to visualize how data is connected in a general way, and when constructing a relational database.

Best Practices

• Identify the entities. The first step in making an ERD is to identify all of the entities you will use. An entity is nothing more than a rectangle with a description of something that your system stores information about. This could be a customer, a manager, an invoice, a schedule, etc. Draw a rectangle for each entity you can think of on your page. Keep them spaced out a bit.
• Identify relationships. Look at two entities, are they related? If so draw a solid line connecting the two entities.
• Describe the relationship. How are the entities related? Draw a diamond between the two entities on the line you just added. In the diamond write a brief description of how they are related.
• Complete the diagram. Continue to connect the entities with lines, and adding diamonds to describe each relationship until all relationships have been described. Each of your entities may not have any relationships, some may have multiple relationships. That is ok.
• Verify accuracy. Consult with all stakeholders to verify accuracy.