Distributed Database Management Systems: Lecture 5

Distributed Database Management Systems: Lecture 5. The main topics covered in this chapter include: data model; legacy data models; a set of tools/constructs used to model a database; record/semantic; relational data model; primary key;...

Distributed Database Management System

Lecture 05

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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, <d1, d2, …,

dn> such that <d1 D1……,

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

Keys

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• Minimum nonempty subset

of a relation whose values uniquely identify each tuple

in relation

Primary Key

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• The superset of the key is

super key, like…

• We also have candidate,

alternate, secondary, foreign

Table

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• Relation represented in a two

dimensional form

pBud pName

pNo

PROJ

eDur eResp

pNo eSal

eTitle eName

eNo

EMP

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eDur eResp

pNo eSal

eTitle eName

eNo

12 7 12 15 10 10

Work Mangr Cons Cons Cons Mangr

P1 P2 P1 P1 P2 P3

500 700 700 850 700 900

Supr Desin Prog Eng Prog Anlyst

Naeem Rahila Narjis Aslam Hafeez Liaqat

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• 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

• Lossless decomposition

• Dependency preservation

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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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• 1NF, attributes have only

atomic values

• 2NF, there are no partial

dependencies

• 3NF, for each XY where Y is

not in X, either X is a superkey

of R or Y is prime attribute