TAILIEUCHUNG - Lecture Database Systems - Lecture 28

This chapter provides an overview of the database-design process, with major emphasis on database design using the entity-relationship data model. The entity-relationship data model provides a high-level view of the issues in database design, and of the problems that we encounter in capturing the semantics of realistic applications within the constraints of a data model. UML class-diagram notation is also covered in this chapter. | CSC271 Database Systems Lecture # 28 Summary: Previous Lecture Purpose of normalization Data redundancy and update anomalies Functional Dependencies Partial, full, transitive Identifying functional dependencies Identifying primary keys using functional dependencies The Process of Normalization Normalization is a formal technique for analyzing relations based on their PK (or CKs) and functional dependencies The technique involves a series of rules that can be used to test individual relations so that a database can be normalized to any degree When a requirement is not met, the relation violating the requirement must be decomposed into relations that individually meet the requirements of normalization Types of normal forms are 1NF, 2NF, 3NF, BCNF, 4NF, 5NF All normal forms are based on FDs except 1NF Normal forms 4NF, 5NF deal with the situations that are very rare The Process of Normalization Normalization is often executed as a series of steps, each step corresponds to a specific normal form that has known properties As normalization proceeds, the relations become progressively more restricted (stronger) in format and also less vulnerable to update anomalies For the relational data model, it is important to recognize that it is only First Normal Form (1NF) that is critical in creating relations; all subsequent normal forms are optional However, to avoid the update anomalies, it is generally recommended that we proceed to at least Third Normal Form (3NF) The Process of Normalization Unnormalized Form (UNF) A table that contains one or more repeating groups To create an unnormalized table Transform the data from the information source (. form) into table format with columns and rows Lease Forms: DreamHome Transformation into UNF Table First Normal Form (1NF) A relation in which the intersection of each row and column contains one and only one value UNF to 1NF Nominate an attribute or group of attributes to act as the key for the unnormalized table Identify the .

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