Chapter 17 Database 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. Copyright © 2012 Pearson Education, Inc. publishing as Prentice Hall 17-2

Database Design Process System Analysis Conceptual Design Physical Design Implementation & Conversion Operation & Maintenance Copyright © 2012 Pearson Education, Inc. publishing as Prentice Hall 17-3

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 Copyright © 2012 Pearson Education, Inc. publishing as Prentice Hall 17-4

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) Copyright © 2012 Pearson Education, Inc. publishing as Prentice Hall 17-6

Entity-Relationship Diagrams  Used to graphically represent a database schema  Depicts entities  Anything an organization wants to collect information about  Relationships between entities Copyright © 2012 Pearson Education, Inc. publishing as Prentice Hall 17-7

E-R Diagram Variations Copyright © 2012 Pearson Education, Inc. publishing as Prentice Hall 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 Copyright © 2012 Pearson Education, Inc. publishing as Prentice Hall 17-9

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. Copyright © 2012 Pearson Education, Inc. publishing as Prentice Hall 17-10

Business Cycle Give–Get Relationships Copyright © 2012 Pearson Education, Inc. publishing as Prentice Hall 17-11

Revenue Cycle REA Diagram Copyright © 2012 Pearson Education, Inc. publishing as Prentice Hall 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. Copyright © 2012 Pearson Education, Inc. publishing as Prentice Hall 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 Copyright © 2012 Pearson Education, Inc. publishing as Prentice Hall 17-14

Three Types of Relationships  Relationship type is based on maximum cardinality:  One-to-One:  One-to-Many:  Many-to-Many: Copyright © 2012 Pearson Education, Inc. publishing as Prentice Hall 17-15