Understanding Entity Types, Instances, and Attributes in ER Database Management, Slides of Introduction to Database Management Systems

Download Understanding Entity Types, Instances, and Attributes in ER Database Management and more Slides Introduction to Database Management Systems in PDF only on Docsity!

Database

Management

System

Lecture - 7

Entity-Relationship

Data Model

Major Components

Entities

Attributes

Relationships

Entity

Term used to mean three different meanings  Entity type  Entity instance  Entity set

Entity Type

Distinguishable from other entity types on the basis of properties

Identified through abstraction process

Different from External EntityDocsity.com

Entity Instance & Set

A particular object belonging to a particular entity type

Entity Type: Employee

Entity Instance: M. Sharif

Entity Set: All employees

Weak Entity Types

An entity type whose instances cannot exist without being linked with instances of some other entity type, i.e., they cannot exist independently

Strong Entity Type

A strong/regular entity type is the one whose instances can exist independently, i.e., without being linked to other instances

Strong ETs have their own identity

Symbols

Regular Entity Type

Weak Entity Type

NAME

NAME

EMPPLOYEE (^) DEPENDENTS

BOOK (^) BOOKCOPY

Attribute

An attribute of an entity type is a defining property or quality of the instances of that entity type. Entity instances of same entity type have the same attributes. (e.g. Student Identification, Student Name) Docsity.com

Types of Attributes

Single vs composite

Single valued vs multi-valued

Stored vs derived

Symbols for Attributes

Each represented as an oval, linked with an ET symbol

Example

EMPLOYEE

Experience empId (^) empName

dateHired emp_Qual street houseNo

address

Thanks