A Foreign Key is an attribute of an entity that is a primary key component in a related entity. The foreign key is the product of a parent/child relationship. It is an attribute of the child entity, but its properties can be changed only in the parent entity.
Most physical properties of the foreign key attribute are identical to the properties of the primary key component from which it is derived. The following properties may be different:
Nullity
The nullity value of the FK is based on the relationship between the parent and child.
Relationship
FK attribute
Identifying
Not null
Non-identifying, parent not optional
Not null
Non-identifying, parent optional
Null
Attribute Name
The name of the foreign key attribute is the same as the name of the primary key attribute in the parent entity, with some exceptions. If a Role Name is specified, the name of the foreign key attribute is the role name.
