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.
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.
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.