3NF is the third normal form; it is defined as the third step in the normalizing of a database, it essentially builds off the first and second normal forms. It states that all columns references that exist in reference data that are not explicitly dependent on the primary key in the given database should be removed. For example, in a table of data in a database containing information of a car parts store, there exists customer number, unit price and quantity as well as the total amount. Ideally, the order number is the primary key in this table. Looking at the data contained in the table, we have to satisfy 1NF and 2NF to move to satisfy 3NF. 1NF requires that there are no duplicates in the table and the presence of a primary key. Looking at the table, these requirements have been satisfied. 2NF requires that there are no subsets of data that apply to exist multiple rows. Looking at the table, these requirements have been satisfied. Moving on to 3NF, the requirements are that all columns ought to be dependent on the primary key. Looking at the table, it is clear that all columns are not fully dependent on the primary key. The total column can be created by multiplying the quantity by unit price. Therefore, the total column is eliminated from the table to enable compliance with 3NF. Order Number Customer Number Unit Price Quantity Total Amount 01 842 50 4 200 02 919 70 7 490 03 376 35 6 210 04 241 40 2 80

By Professor Henry 3 years ago . Marked as helpful (766). Marked as unhelpful (729)