Normalization
A technique for identifying
table structures that have
potential maintenance
problems
Normalization
Normalization is a set of formal conditions
that assure that a database is
maintainable.
The results of a well executed
normalization process are the same as
those of a well planned E-R model
PROCESS OF DATA
NORMALIZATION
 ELIMINATE REPEATING GROUPS
Make a separate table for each set of related attributes
and give each table a primary key.
 ELIMINATE REDUNDANT DATA
If an attribute depends on only part of a multivalued
key, remove it to a separate table.
 ELIMINATE COLUMNS NOT DEPENDENT ON KEY
If attributes do not contribute to a description of the
key, remove them to a separate table.
Database Programming and Design
PROCESS OF DATA
NORMALIZATION
 ISOLATE INDEPENDENT MULTIPLE RELATIONSHIPS
No table may contain two or more 1:n or n:m
relationships that are not directly related.
 ISOLATE SEMANTICALLY RELATED MULTIPLE
RELATIONSHIPS
There may be practical constraints on information that
justify separating logically related many-to-many
relationships.
Database Programming and Design
Anomalies
A table anomaly is a structure for which a
normal database operation cannot be
executed without information loss or full
search of the data table
Insertion Anomaly
Deletion Anomaly
Update or Modification Anomaly
Normal Forms
Relational theory defines a number of
structure conditions called Normal Forms
that assure that certain data anomalies do
not occur in a database.
Normal Forms
1NF
2NF
3NF
BCNF
4NF
Keys; No repeating groups
No partial dependencies
No transitive dependencies
Determinants are candidate keys
No multivalued dependencies
Form
(Company Order History)
Order # 12003
Date Oct 1, 1997
Oklahoma Retail Company
1111 Asp
Norman
1.
2.
3.
Description
Code Qty
Price Amount
Footballs
Sweat Shirts
Shorts
21
44
37
25.00 150
15.00 300
12.00 120
Total
6
20
10
570
0nf: Remove titles and
derived quantities
Order # 12003
Date Oct 1, 1997
Oklahoma Retail Company
1111 Asp
Norman
1.
2.
3.
Description
Code Qty
Price Amount
Footballs
Sweat Shirts
Shorts
21
44
37
25.00 150
15.00 300
12.00 120
Total
6
20
10
570
0 Normal Form


Remove titles and derived quantities
Schema notation
HISTORY(CustName, CustAddr, CustCity
{OrderNum, OrderDate {ProdDescr,
ProdCode, QtyOrdered, OrderPrice}}
1st Normal Form
Add keys
Remove repeating groups
1st Normal Form


Add Keys for embedded entities
Remove Repeating Groups
HISTORY(CustID, CustName, CustAddr,
CustCity {OrderNum, OrderDate {ProdDescr,
ProdCode, QtyOrdered, OrderPrice}}
1st Normal Form


Add Keys for embedded entities
Remove Repeating Groups
Create a table for each embedded entity,
from the outside for nested groups
Insert foreign keys and junction tables
CUSTOMER(CustID, CustName, CustAddr,
CustCity)
ORDER(OrderNum, CustID, OrderDate {ProdDescr,
ProdCode, QtyOrdered, OrderPrice})
1st Normal Form
CUSTOMER(CustID, CustName, CustAddr,
CustCity)
ORDER(OrderNum, CustID, OrderDate)
PRODUCT(ProdDescr, ProdCode,)
ORDER-PRODUCT(OrderNum, ProdCode,
QtyOrdered, OrderPrice)
1st Normal Form
CUSTOMER
ORDER
PRODUCT
1NF
(Keys, No Repeating Groups)
Table contains multi-valued attributes.
TABLE
{ ATTRIBUTES}
TABLE
??
ATTR-TABLE
2nd Normal Form
No partial dependencies
(an attribute has a partial
dependency if it depends
on part of a concatenated
key)
2nd Normal Form
ROSTER(StuID, ZAPNum, StudentName,
CourseTitle, CourseGrade)
Remove partial dependencies
STUDENT(StuID, StudentName)
SECTION(ZAPNum, CourseTitle)
STUDENT-SECTION(StuID, ZAPNum,
CourseGrade)
2nd Normal Form
ROSTER
STUDENT
SECTION
STUDENT-SECTION
2NF
No partial dependencies
Table has data from several connected tables.
TABLE
??
TABLE
??
3rd Normal Form
No transitive dependencies
(a transitive dependency is
an attribute that depends
on other non-key
attributes)
3rd Normal Form
Note: a transitive dependency arises when
attributes from a second entity appear in
a given table.
SECTION(ZAPNum, RoomNum, Day, Time,
CourseTitle, HoursCredit)
3rd Normal Form
SECTION(ZAPNum, RoomNum, Day,
Time, CourseID ,CourseTitle,
HoursCredit)
SECTION(ZAPNum, RoomNum, Day,
Time, CourseID)
COURSE(CourseID, CourseTitle,
HoursCredit)
3NF
No transitive dependencies
Table contains data from an embedded entity with
non-key attributes.
TABLE
TABLE
SUB-TABLE
??
SUB-TABLE
BCNF is the same, but the embedded table may
involve key attributes.
Boyce Codd Normal Form
Every determinant is a
candidate key
BCNF
BCNF dependenceies are like 3nf
dependencies but they involve some key
attributes
Note: BCNF often arises when a 1:m
relationship is modeled as a m:n
relationship
BCNF
SALESMAN-CUST(SalesID, CustID,
Commission)
SALESMAN(SalesID, Commission)
CUSTOMER(CustID, SalesID)
4th Normal Form
No multi-valued
dependencies
4th Normal Form
Note: 4th Normal Form violations occur
when a triple (or higher) concatenated
key represents a pair of double keys
4th Normal Form
4th Normal Form
Multuvalued dependencies
Instructor
Book
Class
Price
Inro Comp
MIS 2003
Parker
Intro Comp
MIS 2003
Kemp
Data in Action
MIS 4533
Kemp
ORACLE Tricks MIS 4533
Warner
Data in Action
Warner
ORACLE Tricks MIS 4533
MIS 4533
4th Normal Form
INSTR-BOOK-COURSE(InstrID, Book,
CourseID)
COURSE-BOOK(CourseID, Book)
COURSE-INSTR(CourseID, InstrID)
4NF
(No multivalued dependencies)
Independent repeating groups have been treated as a
complex relationship.
TABLE
TABLE
TABLE
TABLE
TABLE
TABLE