Distributed Database Management Systems: Lecture 6

Distributed Database
Management System
Lecture 6


First Three Normal Forms
• First Normal Form
• Second Normal Form: we are not
much interested in it. Its more of a
historical perspective
• Third Normal Form: 3NF, for each
XY where Y is not in X, either X is a
superkey of R or Y is prime attribute
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Boyce-Code Normal Form
• BCNF, For every FD X  Y in R,
X is the superkey
• Removal of second part creates
situation where a relation in in
3NF but not in BCNF, vice versa
never happens
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A relation R defined on attributes

A(A1, A2, …., An), if X A, Y A,
Z A, if for each value of X, there is
a unique value of (Y,Z) pair and Z
depends only on X then X
multidetermines Z, X > Z and
also X > Y
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Fourth Normal Form
• If a relation is in BCNF and all
MVDs are also FDs
• EMP-PROJ is broken in
– EMP(eNo, pNo)
– SKILL(eNo, eSkill)

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P-J Dependency
•A relation R defined on attributes
A(A1, A2, …., An), if X A, Y A,
Z A, if R is equal to join of X, Y
and Z then (X, Y, Z) constitute
project-join dependency for R
• A relation R is in 5NF if every join

dependency is implied by the CKs
of R
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Integrity Rules
• Rules to maintain the consistency of
DB
• Structural, Behavioral
• Beh: help to capture semantics of App
• Should be verified at each update,
since updates can lead to
inconsistencies
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