Entity Set

Question

Hi What is Weak Entity set? Thanks

Arjun Panwar · Answer

Thanks to all for this reply

Satyapriya Nayak · Answer

Hi Arjun An entity set that does not have a primary key is referred to as a weak entity set. The existance of a weak entity set depends on the existence of a strong entity set; it must relate to the strong set via a on-to-many relationship set. A distriminator of a weak entity set is the set of attributes that distinguishes among all the entities of a weak entity set. The primary key of a weak entity set is formed by the primary key of the strong entity set on which the weak entity set is existence depend plus the weak entity set's discriminator. Refer http://www.cs.sfu.ca/CourseCentral/354/zaiane/material/slides/Chapter2/tsld024.htm Thanks

Vulpes · Answer

In relational datatbase theory an entity set is said to be 'weak' if it doesn't have enough attributes to uniquely indentify its members and hence to form a primary key. Typically such sets need to use a foreign key in conjunction with the attributes they do have to form a primary key. In contrast an entity set which does have sufficient attributes to uniquely identify its members and to form a primary key is said to be 'strong'.