Data Modeling with ERD BUS 782

Entities An entity is a person, place, object, event, or concept in the user environment about which the organization wishes to maintain data. –Person: Employee, Student, patient –Place: Warehouse, Store –Object: Product, Machine. –Event: Registration, Sale, Renewal –Concept: Account, Course Physical existence: Customer, student, product, etc. Conceptual existence: Bank accounts, sale

Entity Type A collection of entities that share common properties or characteristics. An entity type represents a collection of entities. A business environment may involve many entity types. –University: Faculty, Student, Course –Department, Employee, Dependent –Sales person, Customer, Order

Relationship Relationship: Interaction between entity types. –Faculty teach Course, Faculty advise Student –Customer open Account, Customer purchase Product. Binary relationship: A relationship involves two entity types. Three types of binary relationship: –1:1, 1:M, M:M

Entity-Relationship Diagram ER modeling begins by identifying the entities and relationships between entities that must be represented in the model. In an ERD, an entity type is represented by a rectangle labeled with a singular name. A relationship has a verb phrase name: –Faculty teach Course, Faculty advise Student

M:M Relationship Peter Paul John Woody Alan Mary Linda Nancy Mia Pia A boy may date 0, 1, or many girls. A girl may date 0, 1, or many boys. Note: “Many boys date many girls” is not a correct interpretation. Boy Girl

1:1 Relationship Peter Paul John Woody Alan Mary Linda Nancy Mia Pia A man may marry 0 or 1 woman. A woman may marry 0 or 1 man. Man Woman

1:M Relationship Peter Paul John Woody Alan Mary Brian Linda Aron Nancy Ronald Mia Pia A father has 1 or many children. A child has 1 father. Father Child

Other Examples 1:1 –State, State Governor –Order, Invoice 1:M –Department, Employee –Customer, Order M:M –Bank customer, Bank account –Student, Student organization

ERD Notations Student Account Faculty Course Has 11 Enroll MM Advise M 1 Teach M 1

Alternative Notations Student Account Faculty Course Has Teach Enroll Advise

Attributes Properties of an entity or a relationship. Simple attributes vs Composite attributes –Address:Street address, City, State, ZipCode Single-valued attributes vs multivalued attributes Derived attributes Primary key

Student SID Fname Lname DateOfBirth Age FullName Major

Domains of Attributes The set of allowable values for one or more attributes. Input validation Examples: –Sex: F, M –EmpHourlyWage: Between 6 and 300 –EmpName: 50 charcters

Introduction to Relational Database Data is logically structured within relations. Each relation is a table (file) with named columns (attributes, fields) and rows (records).

Properties of a Relation Simple attribute –No composite, no multivalued attribute Each relation must have a primary key: –Simple or composite key –May have other keys (candidate keys) –Key cannot be null –Cannot be duplicated

Relational Database Design Create a table for each entity that includes all simple attributes Relationship: –1:1, 1:M Relationship table Foreign key –M:M: relationship table

Database Design Example University: –1:1 Relationship: Student and Account –What is Peter’s account balance –Find students that owe more than 2000 dollars. –1:M Relationship Faculty Advisor and student –Who is Peter’s advisor? –How many students advised by Chao? –M:M Relationship Student and course –How many units Peter takes? –Find students that are taking 363.

Database Design Example Bank: –Customer, Account, bank employee

Database Design Example Order Processing: –Customer, Order, Product

AttorneyCase MM CourtJudge AID Aname Phone CID Cname JID Jname M 1 1M CtID Room Hours Phone

Advanced Topics Composite key Multivalued attribute –Student’s Major attribute –Faculty’s DegreeEarned attribute –Vehicle’s Color attribute –Others: PhoneNumber, Address Create a table for each multi-valued attribute Key + attribute Attributes on a relation

Online Shopping Cart Customer ShoppingCart Product Has 1 M M M CID Cname Addr CartIDDate PID Pname Price Phone

Order Form

Online Shopping Cart Customer ShoppingCart Product Has 1 M M M CID Cname Addr CartIDDate Qty PID Pname Price Phone

Attributes on Relationship Examples: –Student/Course: Grade –Order/Product: Quantity

Suggested Readings relationship_model eadings/erd.htmhttp://faculty.babson.edu/osborn/mis7510/r eadings/erd.htm design.htmlhttp://dhdurso.org/articles/database- design.html database-design#