Chapter 3 PHYSICAL DATABASE DESIGN AND IMPLEMENTATION 141
Chapter 3 PHYSICAL DATABASE DESIGN AND IMPLEMENTATION 141 FIGURE 3.6 Create Relationship options dialog as seen from the table diagram window. Utilizing referential integrity guidelines helps maintain the accuracy of data entered into the system. A database system uses referential integrity rules to prohibit subsidiary elements from being entered into the system unless a matching unique element is in the referenced table. The system also protects the data from changes and deletions, assuming that cascading actions (defined later in this chapter) have been carefully and properly implemented. Primary and Foreign Keys The definition of a Primary Key for each table, though not a requirement of the SQL Server database environment, is recommended. A Primary Key helps records maintain their identities as unique rows of a table and also provides a means of relating tables to other tables in the database to maintain normal forms. (For further information on normalization and normal forms, see Chapter 2, Data Modeling. ) A Foreign Key is defined in a subsidiary table as a pointer to the Primary Key or other unique value in the primary table. Both Primary and Foreign Keys are defined in the form of a constraint. The pair of keys work together to accommodate table relationships. A Foreign Key refers back to the Primary Key in the parent table, forming a one-to-one or one-to-many relationship. (To see more about relationships, refer to Chapter 2.)
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