What Is an ERD Notation?
When drawing an ERD (Entity Relationship Diagram), there are several standards for representing entities, relationships, and cardinality. Different notations can make the same data model look very different, so your entire team must use and interpret the same notation consistently.
The three most widely used notations are Crow's Foot (IE), UML Class Diagram, and Peter Chen notation.
Crow's Foot (IE) Notation
The most widely used notation in practice, also known as Information Engineering (IE) notation. Most ERD tools — MySQL Workbench, draw.io, Erdmates — support it by default.
Cardinality Symbols
The shape at the end of a relationship line indicates cardinality:
- Vertical bar: "Exactly one" — mandatory
- Circle: "Zero or one/many" — optional
- Crow's foot: "One or more" — many
One-to-Many Example
One user can have many orders; each order must belong to exactly one user.
Pros and Cons
| Details | |
|---|---|
| Pros | Intuitive at a glance, rich tool support, industry standard |
| Cons | Symbols can feel cryptic to beginners |
UML Class Diagram Notation
Derived from object-oriented design, this notation is familiar to developers. It applies UML's class diagram syntax to data modeling.
Cardinality Symbols
Multiplicity is expressed as numbers or ranges at the end of relationship lines:
1: Exactly one0..1: Zero or one1..*: One or more0..*or*: Zero or more
Pros and Cons
| Details | |
|---|---|
| Pros | Developer-friendly, supports attributes and methods, maps well to ORM |
| Cons | Skews toward class design rather than pure data modeling |
Peter Chen Notation
The original ERD notation proposed by Dr. Peter Chen in 1976. Common in academic settings and well-suited for conceptual data modeling.
Shape Meanings
- Rectangle: Entity
- Ellipse: Attribute
- Diamond: Relationship
- Double Rectangle: Weak Entity
- Double Ellipse: Multi-valued Attribute
Pros and Cons
| Details | |
|---|---|
| Pros | Conceptually precise, academic standard, rich attribute detail |
| Cons | Diagrams become complex; limited modern tool support |
Which Notation Should You Choose?
| Situation | Recommended Notation |
|---|---|
| Production projects, team collaboration | Crow's Foot (IE) |
| Software developer teams | UML Class Diagram |
| Academic data modeling | Peter Chen |
| Explaining to non-developers | Crow's Foot (most intuitive) |
Erdmates Notation Support
Erdmates uses Crow's Foot notation as its default, reflecting the most common real-world practice. Design your ERD visually with AI-powered natural language input, and export SQL DDL directly.
Conclusion
More important than which notation you choose is using it consistently within your team. Whichever standard you adopt, ensure every team member clearly understands what each symbol means and interprets it the same way.