Er Modleing
Entity Relationship (ER) Modeling
In this chapter, you will learn:
½ The main characteristics of entity relationship components ½ How relationships between entities are defined, refined, and incorporated into the database design process ½ How ERD components affect database design and implementation ½ That real-world database design often requires the reconciliation of conflicting goals
4
This chapter expands coverage of the data-modeling aspect of database design. Data modeling is the first step in the database design journey, serving as a bridge between
P
real-world objects and the database model that is implemented in the computer. Therefore, the importance of data-modeling details, expressed graphically through entity relationship diagrams (ERDs), cannot be overstated. Most of the basic concepts and definitions used in the entity relationship model (ERM) were introduced in Chapter 2, Data Models. For example, the basic components of entities and relationships and their representation should now be familiar to you. This chapter goes much deeper and further, analyzing the graphic depiction of relationships among the entities and showing how those depictions help you summarize the wealth of data required to implement a successful design. Finally, the chapter illustrates how conflicting goals can be a challenge in database design, possibly requiring you to make design compromises.
review
F O U R
100
C H A P T E R
4
Note
Because this book generally focuses on the relational model, you might be tempted to conclude that the ERM is exclusively a relational tool. Actually, conceptual models such as the ERM can be used to understand and design the data requirements of an organization. Therefore, the ERM is independent of the database type. Conceptual models are used in the conceptual design of databases, while relational models are used in the logical design of databases. However, because you are now familiar with the relational model
In this chapter, you will learn:
½ The main characteristics of entity relationship components ½ How relationships between entities are defined, refined, and incorporated into the database design process ½ How ERD components affect database design and implementation ½ That real-world database design often requires the reconciliation of conflicting goals
4
This chapter expands coverage of the data-modeling aspect of database design. Data modeling is the first step in the database design journey, serving as a bridge between
P
real-world objects and the database model that is implemented in the computer. Therefore, the importance of data-modeling details, expressed graphically through entity relationship diagrams (ERDs), cannot be overstated. Most of the basic concepts and definitions used in the entity relationship model (ERM) were introduced in Chapter 2, Data Models. For example, the basic components of entities and relationships and their representation should now be familiar to you. This chapter goes much deeper and further, analyzing the graphic depiction of relationships among the entities and showing how those depictions help you summarize the wealth of data required to implement a successful design. Finally, the chapter illustrates how conflicting goals can be a challenge in database design, possibly requiring you to make design compromises.
review
F O U R
100
C H A P T E R
4
Note
Because this book generally focuses on the relational model, you might be tempted to conclude that the ERM is exclusively a relational tool. Actually, conceptual models such as the ERM can be used to understand and design the data requirements of an organization. Therefore, the ERM is independent of the database type. Conceptual models are used in the conceptual design of databases, while relational models are used in the logical design of databases. However, because you are now familiar with the relational model