Represented by a dashed oval. Relationships Mapping between entities. Represented by diamonds. Represented as a line connecting two entities or entity sets. These are descriptive attributes of the relationship.
Entities take on roles in relationship.
Roles are represented by labels on the lines between relationships and entities. Degree of a relationship identifies the number of entities. Binary relationships are most common. Higher-degree relationships can be modeled as a set of binary relationships. Seems obvious, but isn't always.