29+ Design Er Model Relationship Types Example Download Zip PNG. Union types generally mean that the designer has not taken advantage of any common attributes. This entity relationship diagram symbol represents entity types.
A multivalued attribute can have more than one value.
For example, the works_for relationship type in which employees and departments participate. Relationship types associate entity types. Lets assume we have an example article model with relations. It helps to have a diagram showing the entity types and the relations that hold between them.