In the process of identifying primary keys, note whether an entity is strong or weak. If we are able to assign a primary key to an entity, the entity is referred to as being strong. On the other hand, if we are unable to identify a primary key for an entity, the entity is referred to as being weak (see Section 11.4). The primary key of a weak entity can only be identified when we map the weak entity and its relationship with its owner entity to a relation through the placement of a foreign key in that relation. The process of mapping entities and their relationships to relations is described in Step 2.1, and therefore the identification of primary keys for weak entities cannot take place until that step.