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Fifth normal form
(5NF)
o A relation is in 5NF if it is in 4NF
and not contains any join
dependency and joining should be
lossless.
o 5NF is satisfied when all the tables
are broken into as many tables as
possible in order to avoid
redundancy.
o 5NF is also known as Project-join
normal form (PJ/NF).
Example
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SUBJECT LECTURE SEMESTE
R R
Computer Anshika Semester 1
Computer John Semester 1
Math John Semester 1
Math Akash Semester 2
Chemistry Praveen Semester 1
In the above table, John takes both Computer and
Math class for Semester 1 but he doesn't take Math
class for Semester 2. In this case, combination of all
these fields required to identify a valid data.
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Suppose we add a new Semester as Semester 3 but do
not know about the subject and who will be taking
that subject so we leave Lecturer and Subject as
NULL. But all three columns together acts as a
primary key, so we can't leave other two columns
blank.
So to make the above table into 5NF, we can
decompose it into three relations P1, P2 & P3:
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P1
SEMESTER SUBJECT
Semester 1 Computer
Semester 1 Math
Semester 1 Chemistry
Semester 2 Math
P2
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SUBJECT LECTURER
Computer Anshika
Computer John
Math John
Math Akash
Chemistry Praveen
P3
SEMSTER LECTURER
Semester 1 Anshika
Semester 1 John
Semester 1 John
Semester 2 Akash
Semester 1 Praveen
Next TopicDBMS Relational
Decomposition
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