Accounting 6500 Relational Databases: Accounting Applications Introduction to Normalization

Accounting 6500 What is Normalization? The object of normalization is to arrive at an optimal database structure. This “optimal” structure will minimize redundancy in the database. As a result, the integrity of the information in the database will be protected as data are added, modified, and deleted.

Accounting 6500 Why Study Normalization? Effective use of relational database products such as MS Access, SQL Server, Oracle, Sybase, and Informix require knowledge of data structures. Relational systems require that data be properly normalized (i.e. redundancy removed). Normalization provides a method for trouble-shooting a database design.

Accounting 6500 What We Will Learn Today About Normalization How to recognize a poor data structure; How to determine why the data structure is incorrect; How to correct structural errors in the database.

Accounting 6500 Types of Database Relationships One-to-one (Customer ID# ---> Customer Name) One-to-many (Customer ---> Invoice) Many-to-many (Invoice > Products)

Accounting 6500 Example Invoice

Accounting 6500 Prior to Normalization

Accounting 6500 First Normal Form (1NF) There is a one-to-one relationship (correspondence) between the key and the non-key fields.

Accounting NF Violation (Table 1) INV# DATE CUST# CNAME ADDR. 1:1 CAT# DESC QTY PRICE 1:M

Accounting 6500 Table 1(a) Repeating Groups Removed

Accounting 6500 Table 2. Repeating Group File

Accounting 6500 Second Normal Form (2NF) The table satisfies 1NF and All non-key fields are dependent on the whole key. (Relevant only for tables with composite keys)

Accounting NF Violation (Table 2) INV# CAT# DESC QTY PRICE

Accounting 6500 Table 3. (For fields dependent only on CAT#)

Accounting 6500 Table 2(a) Partial Key Dependencies Removed

Accounting 6500 Table 1(a). Revisited (Check 3NF)

Accounting 6500 Third Normal Form The table satisfies 1NF and 2NF and Non-key fields are dependent only on the key.

Accounting 6500 Alternative Definition of Third Normal Form Each non-key field is dependent on the whole key and nothing but the key.

Accounting NF Violation (Table 1(a)) INV# DATE CUST# CNAME ADDR.

Accounting 6500 Table 4. Separate File for Customer Data

Accounting 6500 Table 1(b). Non-primary Key Dependencies Removed

Accounting 6500 The Database in 3NF

Accounting 6500 The Database in 3NF

Accounting 6500 Normalization in Class Exercise Customer#, fname, lname, phone, address,birthday, rental#, rental date, due date, video#, copy #, title, rating, Rental $ assume each video number has multiple copies and each rental $ is determined by video # Remember can rent more than one video at a time Put this information into 3rd normal form identifying primary keys and foreign keys

Accounting 6500 Practical Steps for getting tables into 3NF 1 Divide original table into tables that have related information 2 Select candidate key for each table 3 Analyze each table and check for a 1 NF (no repeating groups--no one to many relationships from key to any non-key attribute b 2 NF (1 NF & each non-key item dependent on whole key- -applies to composite key tables only c 3 NF (2 NF & remove all transitive dependencies--non- key field not determine any other non-key field 4 If have NF violations, fix by dividing out the offending fields into another table--divide and conquer. (May have to iteratively go through steps Connect tables with appropriate foreign keys