Distributed Database Management Systems: Lecture 5

Distributed Database
Management System
Lecture 05


Data Model
• A set of tools/ constructs
used to model a database
• Record/Semantic

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Legacy Data Models
• Hierarchical
• Network
• Relational

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Relational Data Model
• Two major Strengths
• Three Components
• Relational databases based
on relational Data Model

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• A relation R defined over
domains D1, D2, …., Dn is a
set of n-tuples, dn> such that dn Dn
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Schemes in RDB
• EMP(eNo, eName, eTitle,
eSal, pNo, eResp, pDur)
• PROJ(pNo, pName, bud)

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• Each of the attribute in these
two relations has a domain,
like…
• Domains need not to be
distinct

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Keys


Primary Key
• Minimum nonempty subset
of a relation whose values
uniquely identify each tuple
in relation

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• The superset of the key is
super key, like…
• We also have candidate,
alternate, secondary, foreign

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Table


• Relation represented in a two
dimensional form
EMP
eNo eName eTitle eSal pNo eResp eDur

PROJ
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pNo pName pBud
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eNo eName eTitle eSal pNo eResp eDur
E01
E03
E05
E06
E07
E08

Naeem
Rahila
Narjis
Aslam
Hafeez
Liaqat

Supr
Desin
Prog
Eng
Prog
Anlyst

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700
700
850
700
900

P1
P2
P1
P1
P2
P3

Work
Mangr
Cons
Cons
Cons
Mangr

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12
7
12
15
10
10


• After defining a relation’s
scheme, it is populated
• Tuples are rows and
attributes are cols

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• Attributes get values from
same domain
• Can have NULL value,
but….

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Normalization
Step-by-step reversible
process to produce
anomalies free smarter
tables

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• Anomalies Types….
• Major step is decomposition
• Universal Relation approach

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• Three Normal Forms
• BCNF
• Lossless decomposition
• Dependency preservation

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Dependency Structure
• Norm. based on
dependencies
• Up to BCNF on FDs
• MVD and P-JD

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Dependencies
A relation R defined on
attributes A(A1, A2, …., An), if
X A, Y A, if for each value of
X

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there is a unique value in Y,
then X functionally determines
Y, X Y

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• If X Y and there is a Z X
and ZY, then X partially
determines Y or Y is partially
dependent on X

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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

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there is unique value of (Y,Z)
pair and Z depends only on X
then X multidetermines Z,
X
Z

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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
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