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PTADipMgt17. Assignment 1 Group 8 Session 3 Member 1 Entity Relationship Diagrams by Ms Esha Batish. ERD Entity Relationship Diagram. Contents 2. Reasons for ERD Definitions of Entity and Relationship Aspects of ERDs Attributes Model - Kaplan. World English Dictionary
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PTADipMgt17 Assignment 1 Group 8 Session 3 Member 1 Entity Relationship Diagramsby Ms Esha Batish
ERDEntity Relationship Diagram Contents • 2. Reasons for ERD • Definitions of Entity and Relationship • Aspects of ERDs • Attributes • Model - Kaplan
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 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". What is an / noun Entity
Verbs Relationships and Verbs describe Actions or / The Relationship btwn 2 things,Sometimes we need to add a preposition to know the direction of action. Has Owns Buys Purchases Belongs to Works 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 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 • 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. attends STUDENT SCHOOL has
Attributes 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. SCHOOL serves STUDENT Name Name Location Address Tel Tel
Course Enrolled Name I.D. Number STUDENTS enrols
Course Enrolled Name I.D. Number STUDENTS enrols STAFF hires Name Designation I.D number
Course Enrolled Name I.D. Number STUDENTS enrols STAFF hires runs SCHOOLS KLI Name KHEA Designation KHEI I.D number
Washroom Admin Course Enrolled Name Reception Aircon I.D. Number STUDENTS enrols FACILITIES Classroom have has StarHub BRANCHES Address are STAFF Wilkie hires runs SCHOOLS KLI Name KHEA Designation KHEI I.D number
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, LSUStarted 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
