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Database Design. Chapter 2. Goal of all Information Systems. To add value Reduce costs Increase sales or revenue Provide a competitive advantage. Information System (IS) Project Success. On-time Within budget Meets customer’s expectations. IS Project Development.

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goal of all information systems
Goal of all Information Systems
  • To add value
    • Reduce costs
    • Increase sales or revenue
    • Provide a competitive advantage
information system is project success
Information System (IS) Project Success
  • On-time
  • Within budget
  • Meets customer’s expectations
is project development
IS Project Development
  • Model – a simplified view of a real-world system
  • Three common types of models
    • Process models (data flow diagrams)
    • Class or object models*
    • Event models (sequence charts which show timing of events)
initial steps in database design
Initial Steps in Database Design
  • Identify the exact goals of the system.
  • Talk with the users to identify the basic forms (inputs) and reports (outputs).
  • Identify the data items to be stored.
  • Design the classes (tables) and relationships.
  • Identify any business constraints.
  • Verify the design matches the business rules.
important reminder
Important Reminder
  • Business rules are very important. For example:
    • There is a single individual designated as the order placer for each company purchasing products from your organization
    • A customer’s order cannot be placed until all outstanding bills have been paid
    • Customer’s address and phone number must be on file before an order can be placed
identifying user requirements
Identifying User Requirements
  • Interview users
  • Observe operations in the firm
  • Review forms and reports
business objects
Business Objects
  • All business deal with entities or objects
    • Customers
    • Products
    • Employees
    • Sales
  • When developing IS systems, we use the term entity to describe some item in the real world that we wish to track
entities classes
Entities/Classes

Customer

Name

CustomerID

LastName

FirstName

Phone

Address

City

State

ZIP Code

Attributes or Properties

Methods

(optional for database)

Add Customer

Delete Customer

*In relational databases, tables represent each class with attributes being

reported in columns and individual entries being stored in rows (tuples)

primary keys
Primary Keys
  • Every database table must have a primary key so that tables can be linked
  • The primary key must be a unique identifier for each entry (row) in the table
    • Name is not a unique identifier
    • Don’t use SSN
associations and relationships among entities classes
Associations and Relationships among Entities (classes)
  • Cardinality Constraint identifies:
    • The number of instances (multiplicity) one entity can be associated with another
      • One-to-one
      • One-to-many
      • Many-to-many
    • Whether the association is mandatory or optional
      • Optional association
      • Mandatory association
multiplicity
Multiplicity

Examples:

*

1

Order

Customer

Each customer can place many orders

An order is placed by 1 customer

*

*

Employee

Tasks

Each employee can perform several tasks

Tasks can be completed by several different employees

mandatory
Mandatory?

Examples:

0

1

Order

Customer

A customer does not have to place an order

An order must be placed by a customer

1

1

Employee

Tasks

Each employee must perform tasks

Tasks must be completed by an employee

alternate terminology
Alternate Terminology

1…1

0…*

Customer

Order

Mandatory-One

Optional-Many

many to many n ary associations
Many-to-Many (N-ary) Associations
  • When two or more classes have a many-to-many association
  • Must be eliminated by adding a new entity called an associative entity
n ary associations
N-ary Associations

Employee

*

*

Component

*

*

Product

n ary association example
N-ary Association Example

Employee

Name

...

1

*

Assembly

1

*

*

1

Component

CompID

Type

Name

Product

ProductID

Type

Name

Assembly

EmployeeID

CompID

ProductID

Multiplicity is defined as the number of items that could appear if the other N-1 objects

are fixed. Almost always “many.”