Database Management System Lecture 11: Inheritance and Entity-Relationship Model, Slides of Introduction to Database Management Systems

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Database

Management

System

Lecture - 11

Inheritance

Gen/Spec relationship results inheritance between supertype and subtypes

Subtypes inherit or get all the attributes of supertype

Super/Subtype Relationship

Use/Advantage How to identify  General knowledge  Based on the attributes

Specifying Constraints

Completeness constraint  Total specialization rule  Partial specialization Disjointness constraint  Disjoint rule  Overlap rule

Subtype Discriminator

To determine the subtype of a supertype instance

Place an attribute in the supertype whose value determines the subtype type

Disjoint Discriminator

Summary of the E-R Data Model

A semantic data model

Used for the conceptual

database design

Provides three main structures

Entities, Relationships and

attributes

Regular Entity Type

Weak Entity Type

NAME

NAME

Symbols

Attribute represents a property or characteristic of an ET

Attribute can be

Simple Composite Multi-valued Derived

Relationships are link or association between ETs

Relationships can be unary, binary, ternary or n-ary

Relationships are represented using diamonds linked with participant ETs

Unary, Binary and Ternary Rships