Chapter 17

Chapter 17Database Design Using the REA Data Model

Copyright © 2012 Pearson Education, Inc. publishing as Prentice Hall 17-1

Learning Objectives

Discuss the steps for designing and implementing a database system.

Use the REA data model to design an AIS database.

Draw an REA diagram of an AIS database.

Read an REA diagram and explain what it reveals about the business activities and policies of the organization being modeled.


Database Design Process


The System Analysis Process

Systems Analysis Initial planning to determine the need for and

feasibility of developing a new system Judgments about the proposal’s technological and

economic feasibility Identify user information needs Define the scope of the proposed new system Gather information about the expected number of

users and transaction volumes to make preliminary decisions about hardware and software requirements

Conceptual Design Developing the different schemas for the new

system at the conceptual, external, and internal levels


The System Analysis Process (cont’d)

Physical Design Translating the internal-level schema into the

actual database structures that will be implemented in the new system

New applications are developed

Implementation and Conversion Includes all the activities associated with

transferring data from existing systems to the new database AIS

Testing the new system Training employees

Maintaining the New System

Data Modeling

Process of defining an information system so it represents an organizations requirements

Occurs at two stages of the design process: System analysis Conceptual design

Data models: Data flow diagrams (Chapter 3) Flow charts (Chapter 3) Entity-relationship diagrams (Chapter 17)


Entity-Relationship Diagrams

Used to graphically represent a database schema

Depicts entities Anything an organization wants to collect

information about

Relationships between entities


E-R Diagram Variations

17-8

Resources-Events-Agents Diagram

Developed for designing AIS Categorizing entities into:

Resources Things that have economic value

Events Business activities

Management wants to manage and control

Agents People and organizations that participate in events


REA Diagram Rules

1. Each event is linked to at least one resource that it affects.

2. Each event is linked to at least one other event.

Types of links (relationships): Get events Give events Participation events

3. Each event is linked to at least two participating agents.


Business Cycle Give–Get Relationships


Revenue Cycle REA Diagram

17-11

Developing an REA Diagram

1. Identify the events about which management wants to collect information.

2. Identify the resources affected by each event and the agents who participate in those events.

What economic resource is reduced by the “Give” event? What economic resource is acquired by the “Get” event? What economic resource is affected by a commitment

event?

3. Determine the cardinalities of each relationship.

17-13

Cardinalities

Describe the nature of relationships between entities How many instances of one entity can be

linked to each specific instance of another entity

Minimum can be: 0 or 1 Maximum can be: 1 or Many

17-14

Cardinalities

Copyright 2012 © Pearson Education, Inc. publishing as Prentice Hall 17-15

Three Types of Relationships

Relationship type is based on maximum cardinality:

One-to-One:

One-to-Many:

Many-to-Many:


Documents

Chapter 17