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28 CHAPTER 2 DATA MODELS AND RELATIONAL DATABASES

Vendor# Vendor Vendor Contact Phone# Item# Description Unit
Name Address Name Price
2010 AXA, Inc. 22 Heaven Annie White 234-3435 M-45 Blender $15.99
Wood Drive K-4 iPod $65.00
2011 Sys Co. 2273 Morgan John Doe 655-7512 D-12 LCD projector $560.00
Street
2021 MFS 46 Kings Rachelle 234-7799 M-45 Blender $18.00
Square, #5 Brown K-4 iPod $63.80
2013 Lazard 8 Santa Ana Ed King 734-0109 K-8 DVD player $134.00

2014 XYZ Co. 19 Columbus Lan Lee 878-1888 K-8 DVD player $129.99
FIGURE 2-7 Partial Data in a Vendor Table

the primary key cannot be null. That is, without specific information of a vendor, we cannot
inselt any inventory data. The worst anomaly is the delete anomaly. If Sys Co. is out of busi-
ness and we would like to delete its record from the database, we would accidentally delete
the inventory information of LCD projectors if Sys Co. is the only one selling LCD projec-
tors to the company.

Steps in Normalization

Normalization can be understood and accomplished in stages. Each stage corresponds to a
normal form. In this book, we describe and illustrate the steps to reach first, second, and
third normal forms. The fifth normal form is the highest level of normalization in which
any remaining anomalies are removed.
Step 1: Remove any repeating groups (First Normal Form).
Any repeating groups must be separated into a different table to reach the first normal form.
Repeating groups are those related attributes with multivalued data. In the above-mentioned
vendor table, inventory information of item#, descIiption, and unit pIice is a repeat group.
These columns have multivalued data. Hence, to normalize the vendor table to first normal
form, we need to make Vendor Table 1 two tables: Vendor Table 2 and Inventory Table.
According to Figure 2-7, the attribute of Unit Price is vendor and item specific. Hence, we need
to tentatively exclude this attribute from both tables so that they can reach the fIrst normal
fmill. After Step 1, the logical designs of the two tables are: Vendor Table 2 (Vendor#, Vendor
Name, Vendor Address, Contact Name, Phone#), and Inventory Table (Item#, DescIiption).
Step 2: Remove any partial dependencies (Second Normal Form).
When we normalize a table, we need to make sure the decomposed tables are linked so
data can be retrieved from them. Tentatively, let's use Item# with Vendor# in the vendor
table as a concatenated key so we can add back the attribute of Unit Price to the new vendor
table. This proposed table has a logic design as follows: Vendor Table 3 (Vendor#, Item#,
Vendor Name, Vendor Address, Contact Name, Phone#, Unit Price).
This proposed table has the problem of partial dependency. Partial dependency
7
exists if any non-key attribute is dependent on part, not all, of the primary key. That is,

7Non-key attributes are those attributes that are not the primary key.