Foreign key in a logical model

Architecting and designing > Data modeling > Components of an entity relation diagram > Objects in an ERD > Attributes > Foreign key in a logical model

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.

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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 can 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.