Case 11. Decomposing Weak Entities
When the relationship type of a binary relationship is 1:M between an entity and its weak entity, two tables are required: one for each entity, with the entity key from each entity serving as the primary key for the corresponding table.
Additionally, the entity that has a dependency on the existence of another entity has a primary key that is partially or totally derived from the parent entity of the relationship.
Weak entities must be deleted when the strong entity is deleted.
HOSPITAL (HOSP_ID, HOSP_NAME, HOSP_ADDRESS, ...)
UNIT (HOSP_ID, UNIT_NAME, HEAD_NURSE, ...)