Question

One that doesn't have a key attribute and can't exist on its own in the DB

depicted with a double rectangle
its existence depends on the existence of an independent entity called the owner entity
it's related to the owner set with a total participation; 1 -> many relationships from the owner set to the weak entity set
partial key: attributes that can uniquely identify the entities of a weak entity set; it's a dotted underline
the key of a weak entity set is formed as such (ownerKey, partialKey)
a. Strong entity
b. Weak entity
c. Composite entity
d. Derived entity

Answer 1

The entity described is a weak entity, which lacks a primary key and depends on its owner entity for existence. It's represented with a double rectangle and identified using a combination of the owner's key and its unique partial key.

Step-by-step explanation:

The entity being described in the question fits the definition of a weak entity. It doesn't have a key attribute of its own and relies on an independent entity, known as the owner entity, for its existence. A weak entity is depicted in an Entity-Relationship (ER) diagram as a double rectangle. It is involved in a 1 to many relationship with the owner entity, which this relationship is characterized by total participation of the weak entity in the relationship. Each weak entity is identified by a partial key, which uniquely identifies entities within the same owner entity scope. However, since it doesn't have a full primary key, the unique identification of a weak entity in the database requires combining the partial key with the key of the owner entity (as shown in the format (ownerKey, partialKey)). This attribute is usually illustrated in an ER diagram with a dotted underline to distinguish it from the solid underline used for primary keys of strong entities.