Simplified ERD is designed for fast writing (drawing?) of ERD ideas and is based on Crow's Foot ERD, but with these key differences:
- The arrow heads are easier to remember
- There aren't redundant / badly described arrow heads
- A full entity definition isn't required
Arrow Heads
| symbol | description / designation |
|---|---|
---|O | zero or one |
--||O | zero or more |
----| | exactly one |
---|| | one or more |
Examples
Example 1
- Users each have exactly one language
- Languages can each have many users
user O||----| language
Example 2
- Users each have at least one email address
- Email addresses each have at most one user
user O|----|| email_address