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What is Entity? And also define Weak Entity Set?

Database

Entities are the principle data object about which information is to be collected. Entities are usually recognizable concept, either concrete or abstract, such as person, places, thing or events, which have relevance to the databases. Some specific example of entities are employees, project etc.

Entities are classified as independent of dependent:: As independent entity(strong) is one that does not rely on another for identification. A dependent entity (weak) is one that relies on another for identification.

WEAK ENTITY TYPES OR SET:-
A set of entity is called an entity set. The two types of entity set are:--

  1. Weak entity set: - Collection of dependent or weak entities if called weak entity set. Weak entities are those which dependent upon another. The entity set which does not have sufficient attributes to form a primary key.
  2. Srong entity set: -- Collection of dependent or strong entities is called strong entity set. An entity set that has a primary key is called as strong entity set.

Entity set does not have a primary key is a weak entity set. Each weak set must be a part of one to man relationship set.

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