PTADipMgt17

Assignment 1 Group 8 Session 3 Member 1

Entity Relationship Diagrams

by

Ms Esha Batish

ERD Entity Relationship Diagram

Contents 1.

2. Reasons for ERD 2.

Definitions of Entity and Relationship 3.

4.

5.

Aspects of ERDs Attributes Model - Kaplan

What is an

 World English Dictionary entity (ˈɛntɪtɪ) —

n

, pl

-ties

1.something having real or distinct existence; A thing, esp when considered as independent of other things. 2.existence or being 3.the essence or real nature

Entity

/ noun



FOLDOC (Computing dictionary) entity

< database > In an entity relationship model, an entity is a type of thing being modelled such as "person" or "product". Different entities have different sets of attributes such as "name" or "price" and are connected via relationships like "bought".

Relationships and Verbs

Verbs describe Actions or / The Relationship btwn 2 things,

Sometimes we need to add a preposition to know the direction of action.

Works Adds to Has Works for Works at Is taken from Owns Is being worked by Is divided into Is employed with Buys Is the employee of Is subdivided into Purchases Has been employed from/by Is Multiplied by Belongs to

Note! Entities only have relationships with other Entities!

Why do we do ERDs?

Brainstorm process- 1st stage and will be revisited.

Ensures that no data is overlooked Provides direction to the architecture and design team to start physical database design Easy to understand for database designers / systems analyst / managers and users Symbols are understood by all levels

1.

Direction

Single direction:

Aspects of ERDs

attends

STUDENT SCHOOL

Bi direction: has 2. Optionality and Cardinality: Optionality and Cardinality Symbols at the ends of the relationship lines indicate the optionality and the cardinality of each relationship. “Optionality” expresses whether the relationship is optional or mandatory. “Cardinality” expresses the maximum number of relationships.

What are Attributes ?

An

attribute

is something that further describes an entity, e.g. customer first name, customer last name, or product name. They can be just nouns, adjectives.

SCHOOL

serves

STUDENT Name Name Location Tel Address Tel

enrols Course Enrolled Name STUDENTS I.D. Number

enrols Course Enrolled Name STUDENTS I.D. Number hires STAFF I.D number Name Designation

enrols Course Enrolled Name STUDENTS I.D. Number runs KLI KHEA SCHOOLS KHEI hires STAFF I.D number Name Designation

Washroom Admin Classroom Reception FACILITIES Aircon have StarHub Address are BRANCHES has Wilkie runs KLI KHEA SCHOOLS KHEI enrols Course Enrolled Name STUDENTS I.D. Number hires I.D number STAFF Name Designation

Dr. Peter Chen

He is the originator of the Entity-Relationship Model (ER Model), Adjunct Professor at in the Computer Science Department and Emeritus Professor in the College of Business, LSU Started developing the model in 1978.

Thank you & All the best in the Exams!

     References: http://www.databasedesign.co.uk/bookdatabasesafirstcourse/chap3 /chap3.htm

http://www.information-management-architect.com/entity relationship-diagram.html

http://dictionary.reference.com/browse/entity?s=t http://foldoc.org/entity