Entity-Relationship Diagram Arrow Types

The entity-relationship diagram offers only one connector element - relationship, but it can be depicted with various combinations of caps on the ends depending on its cardinality.

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
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
Min-Max Notation

Bachman Notation

The same combination of cardinalities are 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 arrow on the other side.
  • 1 : 1..N - one-to-one and more relationship - depicted as a full circle on one side and 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
Bachman Notation

ERD Tool

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

New Comment

Comment