MySQL + SQL · Lesson 1
Er Diagram Symbols
ER Diagram Symbols
An ER diagram uses standard shapes. Knowing each symbol is a common 2-3 mark exam question.
The Symbols
| Symbol | Represents |
|---|---|
| Rectangle | Entity |
| Ellipse (oval) | Attribute |
| Diamond | Relationship |
| Double ellipse | Multivalued attribute |
| Dashed ellipse | Derived attribute |
| Underlined ellipse | Key attribute |
| Double rectangle | Weak entity |
Example
Student (rectangle) — has attributes roll_no (underlined oval), name (oval), phone (double oval = multivalued). Student connects to Course through an "enrolls" diamond.
Summary
- Rectangle=entity, ellipse=attribute, diamond=relationship.
- Special: double ellipse=multivalued, dashed=derived, underline=key, double rectangle=weak entity.
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