Minimum Cardinality, Effects - Database Management - Lecture Slides, Slides of Introduction to Database Management Systems

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Database

Management

System

Lecture - 10

Minimum Cardinality

Determines whether the link is compulsory or optional

Important, since it effects the implementation

Cardinality Example

STD HOBBY

STD BOOK

STD COURSE

EMP PROJ

Other Notations

STD BOOK STD^ HOBBY

PROJ EMP

Other Notations

STD 1 M BOOK STD M^1 HOBBY PROJ M M EMP

Other Notations

STD 1 BOOK PROJ EMP

DEPT 1 1 CHAIR

Roles in Relationships

Determine the role ETs play in a relationship

Most of the time is clear from the context, like in STD and COURSE relationship

Roles in Relationships

Two situation when they should be expressed explicitly A one to one relationship Two ETs having more than one relationship

Roles Examples

STD ENROLS^ ENROLMENT ENROLLEDBY COURSE

FACUL- TY HEAD

HEADS HEADED BY

Roles Examples

STD^ FACULTY

STD_TEACH

STD_SUP

Dependencies

A type of constraint

Existence dependency

Identifier dependency

Referential Dependency

Existence Dependency

BOOK BOOK COPY

bkId

bkTitle

bkId

CopyId

Enhancements in E-R Data Model

EE-R Data Model

Different proposals Most common feature is representation of supertypes and subtypes A popular feature of Object Oriented paradigm

Super/Subtypes

Also called generalization/ specialization

Supertype is called a General Entity type whereas subtypes are the specializations

Super/Subtypes

PERSON

STD FAC

ST

ST1 ST2 ST

General Entity Types

Specialized Entity Types Docsity.com

Super/Subtypes

EMP

SALARIED HOURLY

Grade

AnalSal

NoOfHrs

HourlyRate

Super/Subtypes

PERSON

STD FAC

StId

CGPA

Qual

ClsName Grade

Name

Id Address

Database

Management

System

Lecture - 10