Entity-Relationship Diagram Arrow Types

Crow's Foot Notation

You can see various combinations of ERD relations cardinalities and their graphical notation in the picture below.

There are the following relations:

• 1 : 1 - one-to-one relationship
• 1 : 0..1 - one-to-zero or one relationship
• 1 : N - one-to-many relationship
• 1 : 1..N - one-to-one and more relationship
• 1 : 0..N - one-to-zero and more relationship
• N : N - one-to-many relationship
• 1..N : 1..N - one or more to one or more relationship
• 0..N : 0..N - zero or more to zero or more relationship

You can create various combinations of cardinality. The cardinality is depicted on a connector end this way:

• 1 - one - is depicted as a perpendicular line to the connector line.
• 0..1 - zero or one - is depicted as a circle and a perpendicular line to the connector line. The circle is always nearer to the center of the relationship.
• N - many - is depicted as two sloping lines forming an arrow toward the center of the relationship (a reverse arrow).
• 0..N - zero or more - has the same meaning as many, but it emphasizes that there can be also a zero cardinality. It is depicted as a circle and a reverse arrow.
• 1..N - one or more - does not allow zero cardinality. It is depicted as a perpendicular line to the connector followed by a reverse arrow.

Crow's Foot Notation

Min-Max Notation

The min-max notation almost does not need any further explanation. The relationship is always depicted as a simple line. The cardinalities are expressed with the text definitions on the corresponding side.

Min-Max Notation

Bachman Notation

The same combination of cardinalities is depicted in the Bachman Notation. You can see various combinations of ERD relation arrows below:

• 1 : 1 - one-to-one relationship - depicted as full circles on both sides.
• 1 : 0..1 - one-to-zero-or-one relationship - depicted as a full circle on one side and an empty circle on the other side.
• 1 : N - one-to-many relationship - depicted as a full circle on one side and an arrow on the other side.
• 1 : 1..N - one-to-one and more relationship - depicted as a full circle on one side and an arrow and full circle on the other side.
• 1 : 0..N - one-to-zero-or-more relationship - depicted in the same way as 1 : N.
• N : N - one-to-many relationship - depicted with arrows on both sides.
• 1..N : 1..N - one-or-more-to-one-or-more relationship - depicted as full circles and arrows on both sides.
• 0..N : 0..N - zero-or-more-to-zero-or-more relationship - depicted in the same way as N : N.

Bachman Notation

ERD Tool

You can download our ERD tool called Software Ideas Modeler here and draw your ER diagrams using the mentioned notation:

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ERD Tool Example