Web site layout - Figure 4-42 shows the 5NF transformation from single
Monday, August 27th, 2007Figure 4-42 shows the 5NF transformation from single three-field composite primary key table to three semi-related tables, each containing two-field composite primary keys. Why is the term semi-related used? Because the tool used in this book to draw ERDs does not actually allow creation of the ERD shown on the right side of the diagram in Figure 4-42. This is very interesting; however, all texts indicate that the 5NF transformation shown in Figure 4-42 as being true and correct. I still find this interesting, though, and harp back to my previous comments on anything beyond 3NF being commercially impractical and possibly overzealous in the application of design features. Figure 4-42: A 5NF transformation. Figure 4-43 shows the actual data structures that reflect 5NF structure shown at the lower-right of the diagram shown in Figure 4-42. 5th NF Transform 5th NF Transform Employee project employee manager Project_Employee project employee Project_Manager project employee Manager_Employee manager employee 118 Chapter 4
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