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: