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(共15张PPT)
Chapter 17Database Design Using the REA Data Model17-Learning ObjectivesDiscuss 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.17-Database Design Process17-The System Analysis ProcessSystems AnalysisInitial planning to determine the need for and feasibility of developing a new systemJudgments about the proposal’s technological and economic feasibilityIdentify user information needsDefine the scope of the proposed new systemGather information about the expected number of users and transaction volumes to make preliminary decisions about hardware and software requirementsConceptual DesignDeveloping the different schemas for the new system at the conceptual, external, and internal levels17-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 ModelingProcess of defining an information system so it represents an organizations requirementsOccurs at two stages of the design process:System analysisConceptual designData models:Data flow diagrams (Chapter 3)Flow charts (Chapter 3)Entity-relationship diagrams (Chapter 17)17-Entity-Relationship DiagramsUsed to graphically represent a database schemaDepicts entitiesAnything an organization wants to collect information aboutRelationships between entities17-E-R Diagram Variations17-Resources-Events-Agents DiagramDeveloped for designing AISCategorizing entities into:ResourcesThings that have economic valueEventsBusiness activitiesManagement wants to manage and controlAgentsPeople and organizations that participate in events17-REA Diagram RulesEach event is linked to at least one resource that it affects.Each event is linked to at least one other event.Types of links (relationships):Get eventsGive eventsParticipation eventsEach event is linked to at least two participating agents.17-Business Cycle Give–Get Relationships17-Revenue Cycle REA Diagram
17-11
Developing an REA DiagramIdentify the events about which management wants to collect information.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 Determine the cardinalities of each relationship.17-CardinalitiesDescribe the nature of relationships between entitiesHow many instances of one entity can be linked to each specific instance of another entityMinimum can be: 0 or 1Maximum can be: 1 or Many17-Three Types of RelationshipsRelationship type is based on maximum cardinality:One-to-One:One-to-Many:Many-to-Many:17-

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