This time we’re going to compare Chen notation with Crow’s Foot notation. These are the two most popular ways to create entity-relationship diagrams. So fire up the Gleek.io app https://app.gleek.io/ in your browser window. 00:00 Intro 00:24 Chen notation 02:11 Crow's foot notation 03:28 Summary The first example we’ll look at is Chen notation. The default shapes will work fine for this because Chen’s notation system uses rectangles to represent entities and diamonds to represent relationships. For our example, let’s imagine a company personnel database with departments and employees. We can show the relationship between department and employee with two rectangles connected by a diamond. The nature of the relationship is written inside the diamond. The department employs the employee. To display cardinality, Chen notation uses the letter m to indicate many on one side of the relationship. The m simply means any number greater or equal to one. This shows that a department can employ many employees. And if a department can only employ a single employee, we’d use a 1 instead of an m. If an employee can only work for one department, we can show this by adding a 1 on the other side of the relationship link. And finally, to bring it all together, we show both cardinality indicators at the same time. This shows that a department can have many employees, but that an employee can only be employed by one department. Great, so we’ve explained the basics of Chen notation! Now let’s create the same diagram using Crow’s Foot notation. First, select all the code in Gleek and press delete so you can start fresh. To enable Gleek to create Crow’s Foot notation, we need to select the entity-relationship option from the dropdown. Our department and employee example would again be two rectangles, but this time we don’t need any diamond between them. Cardinality is shown by the “crow’s foot” fork on the employee side of the relationship. This shows that there can be many employees. If a department can employ zero employees, but still exist, this can be shown by adding a zero to the line. This shows that it can have none, one, or many employees. We can show that an employee can be employed by one and only one department with two vertical lines. That makes it clear that the value must be one, but cannot be more than one. We can also add a label here to show that an employee “works for” a department. Again, we can bring it all together by showing both labels and cardinality at the same time. As you can see, both the Crow’s Foot and Chen notation systems can show the same information. They just do it in very different ways. Making quick Gleek diagrams is the perfect way to experiment, so be sure to try out both Chen and Crow’s Foot notation in Gleek. Then leave a comment under this video to tell us which notation you use and why. Happy diagramming, Gleek fans!

• published: 20 Sep 2021
• views: 13803