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October 2, 2020

How to Draw an Entity Relationship Diagram

Diagrams for Software Engineering

What is an ERD?

ERD stands for entity relationship diagram. ERDs, also called ER diagrams or ER models, are used to describe data and how pieces of data interact with one another. For this reason, ERDs are extremely important in database design and projects that require a clear structure of all data. In this article, we’ll cover how to draw an entity relationship diagram anywhere, as well as giving you specific steps to create an entity relationship diagram in Gliffy.

Video Tutorial: How to Draw an ER Diagram

Drawing an entity relationship diagram is easier if you choose to use online diagramming software. Check out Gliffy’s ER diagram tool for Confluence and Jira or start a free trial of Gliffy Online.

How to Draw an Entity Relationship Diagram

There are a few basic steps to take to draw an ER diagram anywhere: in Gliffy, with Powerpoint, a whiteboard, or even on the back of a napkin. Here’s the basic order to follow.

1. Determine the Entities in Your ERD

Start by identifying the “what”s in your system or architecture. Entities are represented with a rectangle, and you’ll want to give them plenty of room so that you can add to your diagram in the next steps.

2. Add Attributes to Each Entity

Next, consider the attributes that you need to describe each entity. These are drawn and labeled inside ovals. Connect these to the relevant entity and position your attributes to the outside of your diagram, which leaves room for relationships.

3. Define the Relationships Between Entities

Now, think through the relationships or verbs taking place within your system. The easiest way to do this is to look at each entity and try to connect it to another by saying, “What does the ___ do with the ___.” The customer purchases the phone. The cell service maintains the phone. The cell service creates a bill. The customer pays the bill.

4. Add Cardinality to Every Relationship

The final step for this simple ER diagram is to define the amount of data that will come from each entity. Cardinality is a simple notation that quickly tells your ERD reader whether there are zero, one, many, or some combination of those factors between each entity. Your customer can purchase one or many phones. The cell service maintains many phones. The customer pays one bill.

5. Finish and Save Your ERD

This is just a high-level ER model, but it provides enough detail that you should now have a teammate or partner check your work. One of the best ways to do this is to simply have them try to read your diagram out loud. If they end up telling a different story than you intended, you need to do some tweaking.

Another good step to take is to clean up or polish your diagram — if you were drawing by hand, you might have some stray eraser marks. Take a moment to finalize your diagram by aligning shapes, adding color, or redrawing lines to more clearly connect your entities, attributes, and relationships. All these steps are easy if you’re using an online diagramming tool like Gliffy!