Final answer:
A weak entity set is an entity set that does not have sufficient attributes to form a primary key on its own. It relies on the attributes of another entity set to uniquely identify its instances. A strong entity set on the other hand, has sufficient attributes to form a primary key on its own. Therefore, the correct answer options is a)
Step-by-step explanation:
A weak entity set is an entity set that does not have sufficient attributes to form a primary key on its own. In other words, it relies on the attributes of another entity set to uniquely identify its instances. For example, consider an entity set 'Address' that cannot uniquely identify its instances unless it is associated with an 'Employee' entity set.
On the other hand, a strong entity set has sufficient attributes to form a primary key on its own, meaning it can uniquely identify its instances without relying on another entity set. For example, an entity set named 'Student' may have attributes such as 'student_id', 'name', and 'email', which are enough to uniquely identify each student.
Simple entity set and primary entity set are not commonly used terms in entity-relationship modeling and database design. Therefore, options (c) and (d) are not applicable to describe an entity set that does not have sufficient attributes to form a primary key.