Domain constraints, Database Management System

Domain Constraints

Domain constraints are primarily formed for defining the logically correct values for an attribute of a relation. The relation allows attributes of a relation to be confined to a range of values, for instance, values of an attribute age can be restricted as Zero to 150 or a definite type like integers, etc.

                                                      REDUNDANCY AND ASSOCIATED PROBLEMS

Let us take the subsequent relation STUDENT

Enrolment no

Sname

Address

Cno

Cname

Instructor

Office

050112345

Rahul

D-27, main Road

Ranchi

MCS-011

Problem

Solution

Nayan

Kumar

102

050112345

Rahul

D-27, Main Road

Ranchi

MCS-012

Computer

Organisation

Anurag

Sharma

105

050112345

Rahul

D-27, Main Road

Ranchi

MCS-014

SSAD

Preeti

Anand

103

050111341

Aparna

B-III, Gurgaon

MCS-014

SSAD

Preeti

Anand

103

                                                                           Figure: A state of STUDENT relation

The above relation satisfies the properties of a relation and is said to be in first normal form (or 1NF). Theoretically it is convenient to have all the information in one relation as it is then likely to be simpler to query the database. But the relation over has the following undesirable kinds:

Posted Date: 3/7/2013 1:41:24 AM | Location : United States







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