For each unidirectional one-to-one association, one foreign key will be generated with the same direction as the association. The primary key of parent table will also migrate into child table as its foreign key.
Given two entity classes, Person and Account, and a one-to-one association defined between them. The association is unidirectional and navigates from Person to Account:
The generated reference key will be the following:
The generated foreign key has the same direction as the association direction.
If the association is bidirectional (can navigate in two ways), two foreign keys with both directions will be generated since PowerDesigner do not know which one of the generated table is the parent table or the child table. You need to delete one manually.