9.3 Crow's Foot Notation

Level: 9 | Version: v1.1 | Author: Meptrasoft

Overview

Crow's Foot Notation is a visual notation used in ER diagrams to show how many records can be related between entities.

The main symbols represent:

These symbols can be combined:

||  → Exactly one
O|  → Zero or one
|<  → One or many
O<  → Zero or many

Crow's Foot notation → Shows relationship cardinality.

Consider:

DEPARTMENT |——< EMPLOYEE

This means:

One department can have many employees.

The symbol near DEPARTMENT represents one, while the crow's foot near EMPLOYEE represents many.

Another example:

CUSTOMER ||——O< ORDER

This represents an optional-many relationship on the ORDER side: a customer may have zero or many orders, depending on the business rules.

|  → ONE
O  → OPTIONAL / ZERO
<  → MANY

Bar = One, Circle = Zero, Crow's Foot = Many

|   → ONE
O   → OPTIONAL / ZERO
<   → MANY

||  → MANDATORY ONE
O|  → OPTIONAL ONE
|<  → MANDATORY MANY
O<  → OPTIONAL MANY

Crow's Foot notation represents cardinality and optionality in ER diagrams.
| means one.
O means zero/optional.
< means many.
Symbols can be combined to show relationships such as zero-or-one or zero-or-many.

What is Crow's Foot notation?: It is a visual notation used in ER diagrams to represent relationship cardinality and optionality.
What does the crow's foot mean?: It represents many.
What does a circle mean?: It represents zero or optional participation.
What does a bar mean?: It represents one.

💡 Tip: Test your queries and schema definitions using the in-browser interactive runner above.

|  → ONE
O  → ZERO / OPTIONAL
<  → MANY

Crow's Foot notation makes ER relationships easy to read by showing one, zero, and many visually.

End of Crow's Foot Notation