Explain the difference between a weak and a strong entity set?

Answer 1

An entity set that does not possess sufficient attributes to form a primary key is called a weak entity set. One that does have a primary key is called a strong entity set.

The discriminator (or partial key) of a weak entity set is the set of attributes that distinguishes among all the entities of a weak entity set

The existence of a weak entity set depends on the existence of a identifying entity set. It must relate to the identifying entity set via a total, one-to-many relationship set from the identifying to the weak entity set

We depict a weak entity set by double rectangles in E-R diagram. We underline the discriminator of a weak entity set with a dashed line in E-R diagram.

Answer 2

strong entity is the entity that can stand alone

weak entity cannot be exist alone.

usually strong entity represent an real world entity such as course , student, patient, ward, department, employee,.... etc

but

the weak entity represents the relationship between two entities, so in connot be exist alone, there must be two strong entities that the weak entity will connect.