PTADipMgt17 Assignment 1 Group 8 Session 3 Member 1 Entity Relationship Diagrams by Ms Esha Batish

ERD Entity Relationship Diagram Contents Reasons for ERD Definitions of Entity and Relationship Aspects of ERDs Attributes Model - Kaplan

What is an / noun World English Dictionary entity ( ˈɛ nt ɪ t ɪ ) — 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 FOLDOC (Computing dictionary) FOLDOC (Computing dictionary)entity 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". databaseentity- relationship model Entity

Relationships and Verbs describe Actions or / The Relationship btwn 2 things, Sometimes we need to add a preposition to know the direction of action. Verbs Works for Works at Is being worked by Is employed with Is the employee of Has been employed from/by Adds to Is taken from Is divided into Is subdivided into Is Multiplied by Has Owns Buys Purchases 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

Aspects of ERDs 1. Direction Single direction: Bi direction: 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. STUDENT SCHOOL attends has

What are ? 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. Attributes SCHOOL STUDENT serves Name Location Tel Address Name

STUDENTS Name I.D. Number Course Enrolled enrols

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

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

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

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! Thank you & All the best in the Exams! References: /chap3.htm /chap3.htm /chap3.htm /chap3.htm relationship-diagram.html relationship-diagram.html relationship-diagram.html relationship-diagram.html