Normalization
A technique that organizes data
attributes (or fields) such that they are
grouped to form stable, flexible and
adaptive entities.
5-1
Normal Forms
™ First Normal Form (1NF)
¾There are no attributes (fields) that have more
than one value for a single instance (record) of
the entity.
¾There are no repeating fields
™ Second Normal Form (2NF)
¾1NF
¾The value of all non-primary key fields are
dependent on the full primary key - not just part
of it
5-2
Normal Forms
™ Third Normal Form (3NF)
¾2NF
¾The values of its non-primary key fields are not
dependent on any other non-primary key field
5-3
1
Keys
™ Primary
¾ A field whose values identify one and only one record
in a table
¾ Every ACCESS table must have EXACTLY one primary
key
™ Foreign
¾ A primary key of one table that is included in another
table
¾ Links the records in one database table to another
table
5-4
Steps Of Normalization
1. Remove repeating groups of data fields.
2.
Remove partial dependencies:
If any data fields are dependent upon only
part of the primary key defined for your core
business transaction, split those fields out into a
separate table, using the field(s) upon which they
are dependent as the primary key.
5-5
Steps Of Normalization
3. Remove transitive dependencies:
If any fields are dependent upon a non-key
field, split those fields out into a separate table,
using the non-key field as the primary key.
4.
Remove any field which can be easily derived from
other field(s): If any fields can be derived from
others, remove from database.
5.
Check by drawing/comparing to E-R diagram: is
this model correct/logical?
5-6
2
Non-normalized table
™ In this example, we want to design an order
database.
¾ Identify all fields needed in this database
¾ Which attribute above uniquely identifies each order?
• Order Number is the starting primary key
5-7
Non-normalized table
Original Primary Key: Order Number
™ An order can have many parts. This is a repeating field. What
fields above are more closely related to a part than an order?
Part Number, Number of Parts [quantity ordered], Part
Description, Unit Cost, Supplier Number [for the part], supplier
name, supplier address.
™ Remove these fields and put them into a separate table. Which
one of these fields uniquely identifies the part information?
[Part Number]
™ The Primary Key to the new table will be the original primary
key combined with the new unique identifier (Part Number)
™ When a primary key has two or more parts, it is called a
composite primary key.
5-8
First Normal Form
Primary Key: Order Number
Composite Primary Key: Order Number plus Part Number
5-9
3
Checking Second Normal Form
Primary Key: Order Number
Composite Primary Key: Order Number plus Part Number
™ Look at the second table
¾ If you know a part of the primary key, could you derive
any of the non-keyed fields?
• For example: If you know the part number [part of the
primary key], could you derive the part description, the unit
cost and the supplier information for that part?
• Violation of second normal form
5-10
Checking Second Normal Form
Primary Key: Order Number
Composite Primary Key: Order Number plus Part Number
™ Remove the non-keyed fields from the second table that are
dependent on only part of the primary key and put them in a
new table [Part Description. Unit Cost, Supplier Information]
™ Copy the part of the primary key from which these fields can
be determined into the new table. This field will become the
primary key of the new table.
5-11
Second Normal Form
Primary Key: Order Number
Composite Primary Key: Order Number plus Part Number
Primary Key: Part Number
Notice: I moved the PART table name to the table that had the most
information about the part. The ordered part table name came from the
rules for the ERD. One order can have many parts on it and one part
[product line] can be on many orders.
5-12
4
Checking Third Normal Form
Primary Key: Order Number
Composite Primary Key: Order Number plus Part Number
Primary Key: Part Number
™ Look at the third table: If you know the Supplier
Number [a non-keyed field], you can determine the
supplier name and address [non-keyed fields]
¾ Violation of third normal form
5-13
Checking Third Normal Form
Primary Key: Order Number
Composite Primary Key: Order Number plus Part Number
Primary Key: Part Number
™ Remove the fields that can be determined from the other field from
this table. Put them [supplier name and address] in a new table.
™ Copy the field that determines them from the original table into the
new table [supplier number].
¾ This field will be the primary key of the new table.
5-14
Part 1 of Third Normal Form
Primary Key: Order Number
Composite Primary Key: Order Number plus Part Number
Primary Key: Part Number
Primary Key: Supplier Number
5-15
5
Checking Third Normal Form
Primary Key: Order Number
Primary Key: Supplier Number
Composite Primary Key: Order Number plus Part Number
Primary Key: Part Number
™ The top table has the same violation as before but with the
customer information.
¾ Customer name and address can be determined from the customer
number
¾ Violation of 3rd Normal Form
5-16
CheckingThird Normal Form
Primary Key: Order Number
Primary Key: Supplier Number
Composite Primary Key: Order Number plus Part Number
Primary Key: Part Number
™ Remove the fields that can be determined from the other field from
this table. Put them [cust name, address] in a new table.
™ Copy the field that determines them from the original table into the
new table [customer number].
¾ This field will be the primary key of the new table.
5-17
Third Normal Form
Primary Key: Customer Number
Primary Key: Order Number
Primary Key: Supplier Number
Composite Primary Key: Order Number plus Part Number
Primary Key: Part Number
5-18
6
Draw the ERD for Validation
Orders
Customers
Cust No
Cust Name
Cust Address
1
m Order No
Place
1
Order Date
Delivery Date
Order Total
Customer No
Supplier
Supplier No
Supplier Name
Supplier Address
1
Contain
Locate
M
Parts [Inventory]
Part Number
Part Description
Unit Cost
Supplier No
M
1
M
Locate
Ordered Part
Order No
Part Number
Number of Parts
5-19
Normalized Relation
5-20
7