Entity Relationship Diagram, also known as ERD, ER Diagram or ER model, is a type of structural diagram for use in database design. An ERD contains different symbols and connectors that visualize two important information: The major entities within the system scope, and the inter-relationships among these entities.
And that’s why it’s called “Entity” “Relationship” diagram (ERD)!
When we talk about entities in ERD, very often we are referring to business objects such as people/role (e.g. Student), tangible business objects (e.g. Product), intangible business objects (e.g. Log), etc. “Relationship” is about how these entities relate to each other within the system.
So, when do we draw ERDs? While ER models are mostly developed for designing relational database in terms of concept visualization and in terms of physical database design, there are still other situations when ER diagrams can help. Here are some typical use cases.
(I) Database design – Depending on the scale of change, it can be risky to alter a database structure directly in a DBMS. To avoid ruining the data in a production database, it is important to plan out the changes carefully. ERD is a tool that helps. By drawing ER diagrams to visualize database design ideas, you have a chance to identify the mistakes and design flaws, and to make correction before executing the changes in database.
(II) Database debugging – To debug database issues can be challenging, especially when the database contains many tables, which require writing complex SQL in getting the information you need. By visualizing a database schema with an ERD, you have a full picture of the entire database schema. You can easily locate entities, view their attributes and to identify the relationships they have with others. All these allows you to analyze an existing database and to reveal database problem easier.
(II) Database creation and patching – ERD tool like Visual Paradigm supports database generation tool that can automate the database creation and patching process by means of ER diagrams. So, with this ER Diagram tool your ER design is no longer just a static diagram but a mirror that reflects truly the physical database structure.
(IV) Aid in requirements gathering – Determine the requirements of an information system by drawing a conceptual ERD that depicts the high-level business objects of the system. Such an initial model can also be evolved into physical database model that aids the creation of relational database, or aids in the creation of process map and data flow model.