Fifth Normal Form - Example


Consider the following example:

Traveling Salesman Product Availability By Brand
Traveling Salesman Brand Product Type
Jack Schneider Acme Vacuum Cleaner
Jack Schneider Acme Breadbox
Willy Loman Robusto Pruning Shears
Willy Loman Robusto Vacuum Cleaner
Willy Loman Robusto Breadbox
Willy Loman Robusto Umbrella Stand
Louis Ferguson Robusto Vacuum Cleaner
Louis Ferguson Robusto Telescope
Louis Ferguson Acme Vacuum Cleaner
Louis Ferguson Acme Lava Lamp
Louis Ferguson Nimbus Tie Rack

The table's predicate is: Products of the type designated by Product Type, made by the brand designated by Brand, are available from the traveling salesman designated by Traveling Salesman.

In the absence of any rules restricting the valid possible combinations of Traveling Salesman, Brand, and Product Type, the three-attribute table above is necessary in order to model the situation correctly.

Suppose, however, that the following rule applies: A Traveling Salesman has certain Brands and certain Product Types in his repertoire. If Brand B is in his repertoire, and Product Type P is in his repertoire, then (assuming Brand B makes Product Type P), the Traveling Salesman must offer only the products of Product Type P made by Brand B.

In that case, it is possible to split the table into three:

Product Types By Traveling Salesman
Traveling Salesman Product Type
Jack Schneider Vacuum Cleaner
Jack Schneider Breadbox
Willy Loman Pruning Shears
Willy Loman Vacuum Cleaner
Willy Loman Breadbox
Willy Loman Umbrella Stand
Louis Ferguson Telescope
Louis Ferguson Vacuum Cleaner
Louis Ferguson Lava Lamp
Louis Ferguson Tie Rack
Brands By Traveling Salesman
Traveling Salesman Brand
Jack Schneider Acme
Willy Loman Robusto
Louis Ferguson Robusto
Louis Ferguson Acme
Louis Ferguson Nimbus
Product Types By Brand
Brand Product Type
Acme Vacuum Cleaner
Acme Breadbox
Acme Lava Lamp
Robusto Pruning Shears
Robusto Vacuum Cleaner
Robusto Breadbox
Robusto Umbrella Stand
Robusto Telescope
Nimbus Tie Rack

Note how this setup helps to remove redundancy. Suppose that Jack Schneider starts selling Robusto's products. In the previous setup we would have to add two new entries since Jack Schneider is able to sell two Product Types covered by Robusto: Breadboxes and Vacuum Cleaners. With the new setup we need only add a single entry (in Brands By Traveling Salesman).

Read more about this topic:  Fifth Normal Form

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