How to Turn Requirements into an ER Diagram (Find the Entities) in Visio
Nouns become entities, verbs become relationships. Learn a simple way to turn a written requirement into a crow's foot ER diagram in Visio, with a library loan as the example.
Step by step
- Requirements to ERD. You've got a written requirement and you need a data model. Here's a simple trick. The nouns become entities, and the verbs become relationships. Let's try it in Visio.
- The requirement. The requirement says, a member can borrow many books, and a book can be borrowed many times over the years. I'm using the Crow's Foot stencil.
- Nouns are entities. First noun, member. It becomes an entity, with a key and the details we keep. Second noun, book.
- Check the verb. Now the verb, borrow. A member borrows many books, and a book is borrowed by many members. That's many to many, and a database can't store it directly.
- The verb becomes an entity. So the verb becomes an entity of its own. One borrowing is a loan. It holds both keys, plus the dates.
- Relationships. Connect member to loan. One member has zero or many loans. And book to loan. One book appears on zero or many loans.
- Check it out loud. Now read it back against the requirement. Can a member borrow many books? Yes, through many loans. Can a book be borrowed many times? Yes. The model matches.
- Done. Click away to see the model.
- The method. So, underline the nouns, they become entities. Check every verb, and if it's many to many, turn it into an entity that holds both keys. Then read the model back against the requirement.
