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Unformatted text preview: A data model describes the data that flows through the business processes in an organi- zation. During the analysis phase, the data model presents the logical organization of data without indicating how the data are stored, created, or manipulated so that analysts can focus on the business without being distracted by technical details. Later, during the design phase, the data model is changed to reflect exactly how the data will be stored in databases and files. This chapter describes entity relationship diagramming, one of the most common data modeling techniques used in industry. OBJECTIVES Understand the rules and style guidelines for creating entity relationship diagrams. Be able to create an entity relationship diagram. Become familiar with the data dictionary and metadata. Become familiar with the process of normalization. Understand how to balance between entity relationship diagrams and data flow diagrams. CHAPTER OUTLINE INTRODUCTION During the analysis phase, analysts create process models to represent how the business system will operate. At the same time, analysts need to understand the information that is used and created by the business system (e.g., customer information, order informa- tion). In this chapter, we discuss how the data that flow through the processes are orga- nized and presented. A data model is a formal way of representing the data that are used and created by a business system; it illustrates people, places, or things about which information is captured Introduction The Entity Relationship Diagram Reading an Entity Relationship Diagram Elements of an Entity Relationship Diagram The Data Dictionary and Metadata Creating an Entity Relationship Diagram Building Entity Relationship Diagrams Applying the Concepts at CD Selections Validating an ERD Design Guidelines Normalization Balancing Entity Relationship Diagrams with Data Flow Diagrams Summary A P P E N D I X A Data Modeling 1 and how they are related to each other. The data model is drawn using an iterative process in which the model becomes more detailed and less conceptual over time. During analysis, analysts draw a logical data model, which shows the logical organization of data without indicating how data are stored, created, or manipulated. Because this model is free of any implementation or technical details, the analysts can focus more easily on matching the diagram to the real business requirements of the system. In the design phase, analysts draw a physical data model to reflect how the data will physically be stored in databases and files. At this point, the analysts investigate ways to store the data efficiently and to make the data easy to retrieve. The physical data model (Chapter 8) and performance tuning (Chapter 9) are discussed later in the textbook....
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- Spring '11