Chapter 4 selected reading part 1 - Chapter 4 Logical...

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191 LEARNING OBJECTIVES After studying this chapter, you should be able to: Concisely define each of the following key terms: relation, primary key, composite key, foreign key, null, entity integrity rule, referential integrity constraint, well-structured relation, anomaly, surrogate primary key, recursive foreign key, normalization, normal form, functional dependency, determinant, candidate key, first normal form, second normal form, partial functional dependency, third normal form, transitive dependency, synonyms, alias, homonym, and enterprise key. List five properties of relations. State two essential properties of a candidate key. Give a concise definition of each of the following: first normal form, second normal form, and third normal form. Briefly describe four problems that may arise when merging relations. Transform an E-R (or EER) diagram into a logically equivalent set of relations. Create relational tables that incorporate entity integrity and referential integrity constraints. Use normalization to decompose a relation with anomalies into well-structured relations. INTRODUCTION In this chapter, we describe logical database design, with special emphasis on the relational data model. Logical database design is the process of transforming the conceptual data model (described in Chapters 2 and 3) into a logical data model— one that is consistent and compatible with a specific type of database technology. An experienced database designer often will do logical database design in parallel with conceptual data modeling if he or she knows the type of database technology that will be used. It is, however, important to treat these as separate steps so that you concentrate on each important part of database development. Conceptual data modeling is about understanding the organization—getting the requirements right. Logical database design is about creating stable database structures— correctly expressing the requirements in a technical language. Both are important steps that must be performed carefully. Although there are other logical data models, we have two reasons for emphasizing the relational data model in this chapter. First, the relational data Visit hoffer to view the accompanying video for this chapter. C H A P T E R 4 Logical Database Design and the Relational Model WOW! eBook
192 Part III • Database Design model is by far the one most commonly used in contemporary database applications. Second, some of the principles of logical database design for the relational model apply to the other logical models as well. We have introduced the relational data model informally through simple examples in earlier chapters. It is important, however, to note that the relational data model is a form of logical data model, and as such it is different from the conceptual data models. Thus, an E-R data model is not a relational data model, and an E-R model may not obey the rules for a well-structured relational data model, called normalization

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