Optional Attribute (Entity-Relationship Diagram)

An optional attribute is also called nullable. A nullable attribute can contain a NULL value.

The optional attribute in ER diagram is marked with NULL text.

ERD optional attributes

How to Set Optional Attribute

You can set the attribute as optional using the nullability modifier. Right-click on the desired attribute of the entity in the diagram editor and choose Nullable from the context menu.

Set optional attribute in ERD entity

Optional Attribute in Chen Entity-Relationship Diagram

The Chen ERD diagrams do not support specific notation for optional and required attributes. Optionally, you can differentiate between optional and required attributes using the different styles.

Suggested (non-standard) marking of optional attributes in ERD Chen diagram using different styles