chapter06

chapter06 - Concepts of Database Management, Fifth Edition...

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Concepts of Database  Concepts of Database  Management, Fifth Edition Management, Fifth Edition Chapter 6:  Chapter 6:  Database Design 2: Database Design 2: Design Methodology Design Methodology
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2 Objectives Discuss the general process and goals of database design Define user views and explain their function Define database design language and use it to document database designs Create an entity-relationship diagram to visually represent a database design Present a methodology for database design at the information level and view examples illustrating this methodology
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3 Objectives Explain the physical-level design process Discuss top-down and bottom-up approaches to database design and examine the advantages and disadvantages of both methods Use a survey form to obtain information from users prior to beginning the database design process Review existing documents to obtain information prior to beginning the database design
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4 Objectives Discuss special issues related to implementing one-to-one relationships and many-to-many relationships involving more than two entities Discuss entity subtypes and their relationships to nulls Learn how to avoid potential problems when merging third normal form relations Examine the entity-relationship model for representing and designing databases
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5 Database Design Information-level Design – building a database that satisfies the organization’s requirements as cleanly as possible Physical-level design – designers transform the information-level design into a design for the specific DBMS used by the organization User Views – requirements necessary to support a particular user’s operations Cumulative design – supports all user views encountered so far in the design process
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6 Information-Level Design Methodology Information-level Design Methodology Represent user view as collection of tables Normalize these tables Identify all keys Merge the result into design
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7 Represent User View as Collection of Tables Step 1: Determine entities involved and create separate table for each type Step 2: Determine primary key for each table Step 3: Determine properties for each entities Step 4: Determine relationships among entities
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8 Types of Relationships One-to-Many Relationships – created by including the primary key of the “one” table as a foreign key in the “many” table Many-to-Many Relationships – created with a new table whose primary key is the combination of the primary keys of the original tables One-to-One Relationship – created with a single relationship from one record in a table to a single record in another table
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9 Normalize the Tables Represent all keys Primary, alternate, secondary, foreign Database Design Language (DBDL) Mechanism for representing tables and keys DBDL Example Figure 6.1
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chapter06 - Concepts of Database Management, Fifth Edition...

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