Relationship strength is based on how the primary key of a related entity is defined.
Weak Relationships (non-identifying relationship)
- Exists if the PK of the related entity does not contain a PK component of the parent entity.
- Customer(custid, custname)
- Order(orderID, custid, date)
Strong Relationship (identifying)
- Exists when the PK of the related entity contains the PK component of the parent entity.
- Course(CrsCode, DeptCode, Description)
- Class(CrsCode, Section, ClassTime…)