Question

Explain the difference between an independent entity and a dependent entity and explain how the two types are differentiated on the data model.

Answer 1

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Independent entity which is also referred to as Kernel is the base relation (table) upon which other relations (tables) are based on, thus it is the database backbone. While dependent entity is an entity which is based upon the existing independent entities, it derives its value from the independent entities.

Independent entity has the following distinguishing characteristics which makes it different from dependent entity which is:-

Independent entity is the building blocks of any database since other relations/tables cannot exists if it doesn’t exist; that is other relations of the database cannot exist if there is no independent entity since dependent entities reference the independent entity in order for them to make their data meaningful and useful. Therefore for a database to exist there must be an independent entity and for a dependent entity to exist there must be an independent entity but for an independent entity or database to exist, it is not a must there be a dependent entity.

Independent entity has primary key which can be either simple or composite depending on the availability of unique columns in the entity which are not foreign key of any other relation. While a dependent entity primary key can be simple, composite, which can be a foreign key used to establish a relationship with a base entity.

Independent entity has a primary key which is not a foreign key in the entity since an independent entity is always referenced by the dependent entities and, it can never be the independent entity referencing the independent entities. Hence the reason as to why a base relation cannot have a primary key which is a foreign key in it. While dependent entity can have primary key which are foreign keys used to establish a relationship with the base entity.

Independent entity does not depend on other entities which are in the database for it to exist as it is the case with dependent variables which depend on independent entity for their existence. If there is no independent entity in a database then it is not possible to have dependent entities, but independent entity can exist on its own in a database