Entity Set Keys
How to distinguish between entities in an entity set or between relationships in a relationship set?
Super keys: Sets of attributes that allow us to identify uniquely an entity in the entity set.
Candidate key: Minimal sets of such attributes.
Primary key: Candidate key chosen by database designer.
Notation in E-R diagram: primary keys are underlined.
Any two individual entities in the set are prohibited from having the same values on the key attributes at the same time.
The primary key in a relationship set is a combination of the primary keys of all entity sets participating in the relationship set.