How often have you wondered about the structure of an existing database? It could be a 5-year-old legacy system or a brand-new open-source project. Let’s take a look at the ERD diagram of the database behind the most famous content management system: WordPress. What Is WordPress and How Does It Work? WordPress is an open-source CMS (content management system) that was initially released in 2003. It started out as a blogging platform, but it has developed so much that today it can be used for almost anything.