Nonidentifying Relationships

A nonidentifying relationship also connects a parent entity to a child entity. But, when a nonidentifying relationship connects two entities, the foreign key migrates to the nonkey area of the child entity (below the line).

A dashed line connecting the entities indicates a nonidentifying relationship. If you connect the TEAM and PLAYER entities in a nonidentifying relationship, the �team id� migrates to the nonkey as shown in the following figure:

Because the migrated keys in a nonidentifying relationship are not part of the primary key of the child, nonidentifying relationships do not result in any identification dependency. In this case, PLAYER is considered an independent entity, just like TEAM.

However, the relationship can reflect existence dependency if the business rule for the relationship specifies that the foreign key cannot be NULL (missing). If the foreign key must exist, this implies that an instance in the child entity can only exist if an associated parent instance also exists.

Identifying and nonidentifying relationships are not a feature of the IE methodology. These relationships are included in your diagram as a solid or dashed relationship line to help ensure compatibility between IE and IDEF1X methods.