NORMALIZATION

What is Normalization  The process of effectively organizing data in a database  Two goals  To eliminate redundant data  Ensure data dependencies make sense  Guidelines are called normal forms  There are 1 thru 6  They are guidelines - not cast in concrete

1 st Normal form  Written as 1NF  Eliminates duplicate column from the same table  Creates separate tables for each group of related data  Identifies each row with a unique column or set of columns – Primary Key

2 nd Normal Form  Must meet all first normal form requirements  Removes subsets of dta that apply to multiple rows of a table and puts them in separate tables  Creates relationships between these new tables and their predecessors thru the use of Foreign Keys

3 rd Normal Form  Meets all the requirements of second normal form  Removes columns that are not dependent upon the primary key

4 th Normal Form – Boyce Codd  Meets all the requirements of the 3 rd normal form  Has no multi-valued dependencies

5 th Normal Form  Fifth normal form deals with cases where information can be reconstructed from smaller pieces of information that can be maintained with less redundancy.  Second, third, and fourth normal forms also serve this purpose, but fifth normal form generalizes to cases not covered by the others.

6 th Normal Form  Must be in 5 th normal form  Sixth normal form is intended to decompose relation variables to irreducible components.  Though this may be relatively unimportant for non-temporal relation variables, it can be important when dealing with temporal variables or other interval data.  For instance, if a relation comprises a supplier's name, status, and city, we may also want to add temporal data, such as the time during which these values are, or were, valid (e.g. for historical data) but the three values may vary independently of each other and at different rates.  We may, for instance, wish to trace the history of changes to Status.

Primary Key  The primary key of a table must be unique to identify the record in the table.  It's also possible to have a table with a primary key made up of two or more columns.  This occurs when a single column can't contain enough unique values.  For example, a two column primary key might consist of a "FirstName" and "LastName" column.

Foreign Key  A foreign key is a field (or fields) that points to the primary key of another table.  The purpose of the foreign key is to ensure referential integrity of the data.  Customer table – customer Id is the primary key  In an Orders table – the customer id is the foreign key