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Nested relation -oocomputer world

 Nested relation 

 During the first normal form we require that all attributes have atomic domain a domain is atomic if elements of the domain are considered to be indivisible unit. 

For example the set of integer is an atomic domain but the set of all sets of integer is a non atomic domain. We considered set of integer to have subpart the important issue in first normal form not the domain itself but rather the way we use domain element in database. The nested relational model is a extension of the relation model in which domain may be either atomic or relation  valued of a tuple on a attribute may be relation and relation may be stored within relation . A complex objects can be represented by a single tuple of a nested relation if we view a tuple of a nested relation a data item we have a one to one correspondence between data item and objects in the user's view of the database.

 Nested relation are just one example of extensions to the basic relational model. The object oriented data model has caused a need for features such as inheritance and reference to objects complex type  system and object orientation enable ER  model concepts such as entity of entities, multi-valued attribute and generalization and specialization to be represented directly without a complex translation to the relational model.


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