Define and explain the following terms with an example for each Database Management Systems 10CS54 VTU notes 8 Marks Dec Jan 2013 Jun July2014

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Asked by:Nikhil-bharadwaj

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Extension

The extension of a given relation is the set of tuples appearing in that relation at any given instance. The extension thus varies with time. It changes as tuples are created, destroyed, and updated.

Relation: Employee at time= t1
EmpNoEmpNameAgeDept
1001Jason23SD
1002William24HR
1003Jonathan28Fin
1004Harry20Fin

Relation: Employee at time= t2 after adding more records
EmpNoEmpNameAgeDept
1001Jason23SD
1002William24HR
1003Jonathan28Fin
1004Harry20Fin
1005Smith22HR
1006Mary19HR
1007Sarah23SD

Relation: Employee at time= t2 after adding more records
EmpNoEmpNameAgeDept
1001Jason23SD
1002William24HR

Intension

The intension of a given relation is independent of time. It is the permanent part of the relation. It corresponds to what is specified in the relational schema. The intension thus defines all permissible extensions. The intension is a combination of two things : a structure and a set of integrity constraints.

The naming structure consists of the relation name plus the names of the attributes (each with its associated domain name).

The integrity constraints can be subdivided into key constraints, referential constraints, and other constraints.

For example,

Employee(EmpNo Number(4) Not NULL, EName Char(20), Age Number(2), Dept Char(4) )

This is the intension of Employee relation.


Answerd By:Rohit498

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