To become a good data modeler, you need to understand the notation in entity relationship diagrams and apply the notation on problems of increasing complexity. To help you master the notation, this chapter presents the symbols used in entity relationship diagrams and compares entity relationship diagrams to relational database diagrams that you have seen in previous chapters. This chapter then probes deeper into relationships, the most distinguishing part of entity relationship diagrams. You will learn about identification dependency, relationship patterns, and equivalence between two kinds of relationships. Finally, you will learn how to represent similarities among entities using generalization hierarchies.
To provide a deeper understanding of the Crow's Foot notation, business rule representation and diagram rules are presented. To provide an organizational focus on entity relationship diagrams, this chapter presents formal and informal representation of business rules in an entity relationship diagram. To help you use the Crow's Foot notation correctly, this chapter presents consistency and completeness rules and explains their usage in the ER Assistant.
Because of the plethora of entity relationship notations, you may not have the opportunity to use the Crow's Foot notation exactly as shown in Chapters 5 and 6. To prepare you for understanding other notations, the chapter concludes with a presentation of diagram variations including the Class Diagram notation of the Unified Modeling Notation, one of the popular alternatives to the Entity Relationship Model. This chapter provides the basic skills of data modeling to enable you to understand the notation of entity relationship diagrams. To apply data modeling as part of the database development process, you should study Chapter 6 on developing data models for business databases. Chapter 6 emphasizes the problem-solving skills of generating alternative designs, mapping a problem statement to an entity relationship diagram, and justifying design decisions. With the background provided in both chapters, you will be prepared to perform data modeling on case studies and databases for moderate-size organizations.