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

Q) Explain the difference between a weak and a strong entity set.

Answer :

A strong entity set has a primary key. All tuples in the set are distinguishable by that key. A weak entity set has no primary key unless attributes of the strong entity set on which it depends are included. Tuples in a weak entity set are partitioned according to their relationship with tuples in a strong entity set. Tuples within each partition are distinguishable by a discriminator, which is a set of attributes.

Q) We can convert any weak entity set to a strong entity set by simply adding appropriate attributes.Why, then, do we have weak entity sets?

Answer :

We have weak entities for several reasons:

•  We want to avoid the data duplication and consequent possible inconsistencies caused by duplicating the key of the strong entity.


•  Weak entities reflect the logical structure of an entity being dependent on another entity.


•  Weak entities can be deleted automatically when their strong entity is deleted.


• Weak entities can be stored physically with their strong entities.

Related Topics : E-R diagram for favourite sports team statistics

E-R diagram for marks database

E-R diagram for a university

Explain the distinctions among the terms primary key, candidate key, and superkey.

List six major steps that you would take in setting up a database for a particular enterprise.