2021/8/8 Chapter 12 Normalization – Database Design – 2nd Edition
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DATABASE DESIGN – 2ND EDITION
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Chapter 12 Normalization
ADRIENNE WA�
Normalization should be part of the database design process. However, it is dif�cult
to separate the normalization process from the ER modelling process so the two
techniques should be used concurrently.
Use an entity relation diagram (ERD) to provide the big picture, or macro view, of an
organization’s data requirements and operations. This is created through an iterative
process that involves identifying relevant entities, their attributes and their
relationships.
Normalization procedure focuses on characteristics of speci�c entities and repre-
sents the micro view of entities within the ERD.
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What Is Normalization?
Normalization is the branch of relational theory that provides design insights. It is
the process of determining how much redundancy exists in a table. The goals of nor-
malization are to:
Be able to characterize the level of redundancy in a relational schema
Provide mechanisms for transforming schemas in order to remove redundancy
Normalization theory draws heavily on the theory of functional dependencies. Nor-
malization theory de�nes six normal forms (NF). Each normal form involves a set of
dependency properties that a schema must satisfy and each normal form gives guar-
antees about the presence and/or absence of update anomalies. This means that
higher normal forms have less redundancy, and as a result, fewer update problems.
Normal Forms
All the tables in any database can be in one of the normal forms we will discuss next.
Ideally we only want minimal redundancy for PK to FK. Everything else should be
derived from other tables. There are six normal forms, but we will only look at the
�rst four, which are:
First normal form (1NF)
Second normal form (2NF)
Third normal form (3NF)
Boyce-Codd normal form (BCNF)
BCNF is rarely used.
First Normal Form (1NF)
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In the �rst normal form, only single values are permitted at the intersection of each
row and column; hence, there are no repeating groups.
To normalize a relation that contains a repeating group, remove the repeating group
and form two new relations.
The PK of the new relation is a combination of the PK of the original relation plus an
attribute from the newly created relation for unique identi�cation.
Process for 1NF
We will use the Student_Grade_Report table below, from a School database, as our
example to explain the process for 1NF.
Student_Grade_Report (StudentNo, StudentName, Major, CourseNo,
CourseName, InstructorNo, InstructorName, InstructorLocation, Grade)
In the Student Grade Report table, the repeating group is the course informa-
tion. A student can take many courses.
Remove the repeating group. In this case, it’s the course information for each
student.
Identify the PK for your new table.
The PK must uniquely identify the attribute value (StudentNo and CourseNo).
After removing all the attributes related to the course and student, you are left
with the student course table (StudentCourse).
The Student table (Student) is now in �rst normal form with the repeating
group removed.
The two new tables are shown below.
Student (StudentNo, StudentName, Major)
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StudentCourse (StudentNo, CourseNo, CourseName, InstructorNo, In-
structorName, InstructorLocation, Grade)
How to update 1NF anomalies
StudentCourse (StudentNo, CourseNo, CourseName, InstructorNo, InstructorName,
InstructorLocation, Grade)
To add a new course, we need a student.
When course information needs to be updated, we may have inconsistencies.
To delete a student, we might also delete critical information about a course.
Second Normal Form (2NF)
For the second normal form, the relation must �rst be in 1NF. The relation is auto-
matically in 2NF if, and only if, the PK comprises a single attribute.
If the relation has a composite PK, then each non-key attribute must be fully depen-
dent on the entire PK and not on a subset of the PK (i.e., there must be no partial de-
pendency or augmentation).
Process for 2NF
To move to 2NF, a table must �rst be in 1NF.
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The Student table is already in 2NF because it has a single-column PK.
When examining the Student Course table, we see that not all the attributes are
fully dependent on the PK; speci�cally, all course information. The only attribute
that is fully dependent is grade.
Identify the new table that contains the course information.
Identify the PK for the new table.
The three new tables are shown below.
Student (StudentNo, StudentName, Major)
CourseGrade (StudentNo, CourseNo, Grade)
CourseInstructor (CourseNo, CourseName, InstructorNo, Instructor-
Name, InstructorLocation)
How to update 2NF anomalies
When adding a new instructor, we need a course.
Updating course information could lead to inconsistencies for instructor
information.
Deleting a course may also delete instructor information.
�ird Normal Form (3NF)
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To be in third normal form, the relation must be in second normal form. Also all tran-
sitive dependencies must be removed; a non-key attribute may not be functionally
dependent on another non-key attribute.
Process for 3NF
Eliminate all dependent attributes in transitive relationship(s) from each of the
tables that have a transitive relationship.
Create new table(s) with removed dependency.
Check new table(s) as well as table(s) modi�ed to make sure that each table has a
determinant and that no table contains inappropriate dependencies.
See the four new tables below.
Student (StudentNo, StudentName, Major)
CourseGrade (StudentNo, CourseNo, Grade)
Course (CourseNo, CourseName, InstructorNo)
Instructor (InstructorNo, InstructorName, InstructorLocation)
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At this stage, there should be no anomalies in third normal form. Let’s look at the de-
pendency diagram (Figure 12.1) for this example. The �rst step is to remove repeating
groups, as discussed above.
Student (StudentNo, StudentName, Major)
StudentCourse (StudentNo, CourseNo, CourseName, InstructorNo, InstructorName,
InstructorLocation, Grade)
To recap the normalization process for the School database, review the dependen-
cies shown in Figure 12.1.
Figure 12.1 Dependency diagram, by A.
Watt.
The abbreviations used in Figure 12.1 are as follows:
PD: partial dependency
TD: transitive dependency
FD: full dependency (Note: FD typically stands for functional dependency. Us-
ing FD as an abbreviation for full dependency is only used in Figure 12.1.)
Boyce-Codd Normal Form (BCNF)
When a table has more than one candidate key, anomalies may result even though
the relation is in 3NF. Boyce-Codd normal form is a special case of 3NF. A relation is
in BCNF if, and only if, every determinant is a candidate key.
BCNF Example 1
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Consider the following table (St_Maj_Adv).
Student_id Major Advisor
111 Physics Smith
111 Music Chan
320 Math Dobbs
671 Physics White
803 Physics Smith
The semantic rules (business rules applied to the database) for this table are:
���Each Student may major in several subjects.
���For each Major, a given Student has only one Advisor.
���Each Major has several Advisors.
���Each Advisor advises only one Major.
���Each Advisor advises several Students in one Major.
The functional dependencies for this table are listed below. The �rst one is a candi-
date key; the second is not.
���Student_id, Major ——> Advisor
���Advisor ——> Major
Anomalies for this table include:
���Delete – student deletes advisor info
���Insert – a new advisor needs a student
���Update – inconsistencies
Note: No single attribute is a candidate key.
PK can be Student_id, Major or Student_id, Advisor.
To reduce the St_Maj_Adv relation to BCNF, you create two new tables:
���St_Adv (Student_id, Advisor)
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���Adv_Maj (Advisor, Major)
St_Adv table
Student_id Advisor
111 Smith
111 Chan
320 Dobbs
671 White
803 Smith
Adv_Maj table
Advisor Major
Smith Physics
Chan Music
Dobbs Math
White Physics
BCNF Example 2
Consider the following table (Client_Interview).
ClientNo InterviewDate InterviewTime StaffNo RoomNo
CR76 13-May-02 10.30 SG5 G101
CR56 13-May-02 12.00 SG5 G101
CR74 13-May-02 12.00 SG37 G102
CR56 1-July-02 10.30 SG5 G102
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FD2 – staffNo, interviewDate, interviewTime –> clientNO (candidate key: CK)
FD3 – roomNo, interviewDate, interviewTime –> staffNo, clientNo (CK)
FD4 – staffNo, interviewDate –> roomNo
A relation is in BCNF if, and only if, every determinant is a candidate key. We need to
create a table that incorporates the �rst three FDs (Client_Interview2 table) and
another table (StaffRoom table) for the fourth FD.
Client_Interview2 table
ClientNo InterviewDate InterViewTime StaffNo
CR76 13-May-02 10.30 SG5
CR56 13-May-02 12.00 SG5
CR74 13-May-02 12.00 SG37
CR56 1-July-02 10.30 SG5
StaffRoom table
StaffNo InterviewDate RoomNo
SG5 13-May-02 G101
SG37 13-May-02 G102
SG5 1-July-02 G102
Normalization and Database Design
During the normalization process of database design, make sure that proposed enti-
ties meet required normal form before table structures are created. Many real-world
databases have been improperly designed or burdened with anomalies if improperly
modi�ed during the course of time. You may be asked to redesign and modify exist-
ing databases. This can be a large undertaking if the tables are not properly
normalized.
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Key Terms and Abbrevations
Boyce-Codd normal form (BCNF): a special case of 3rd NF
�rst normal form (1NF): only single values are permitted at the intersection
of each row and column so there are no repeating groups
normalization: the process of determining how much redundancy exists in a
table
second normal form (2NF): the relation must be in 1NF and the PK comprises
a single attribute
semantic rules: business rules applied to the database
third normal form (3NF): the relation must be in 2NF and all transitive de-
pendencies must be removed; a non-key attribute may not be functionally
dependent on another non-key attribute
Exercises
Complete chapters 11 and 12 before doing these exercises.
���What is normalization?
���When is a table in 1NF?
���When is a table in 2NF?
���When is a table in 3NF?
��� Identify and discuss each of the indicated dependencies in the depen-
dency diagram shown in Figure 12.2.
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Figure 12.2 For question 5, by A. Watt.
���To keep track of students and courses, a new college uses the table
structure in Figure 12.3.
Draw the dependency diagram for this table.
Figure 12.3 For question 6, by A. Watt.
���Using the dependency diagram you just drew, show the tables (in their
third normal form) you would create to �x the problems you encoun-
tered. Draw the dependency diagram for the �xed table.
���An agency called Instant Cover supplies part-time/temporary staff to
hotels in Scotland. Figure 12.4 lists the time spent by agency staff
working at various hotels. The national insurance number (NIN) is
unique for every member of staff. Use Figure 12.4 to answer questions
(a) and (b).
Figure 12.4 For question 8, by A. Watt.
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Database Design – 2nd Edition by
Adrienne Watt is licensed under a
Creative Commons Attribution 4.0
International License except where
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���This table is susceptible to update anomalies. Provide examples
of insertion, deletion and update anomalies.
���Normalize this table to third normal form. State any assumptions.
���Fill in the blanks:
���____________________ produces a lower normal form.
���Any attribute whose value determines other values within a row
is called a(n) ____________________.
���An attribute that cannot be further divided is said to display
____________________.
���____________________ refers to the level of detail repre-
sented by the values stored in a table’s row.
���A relational table must not contain
____________________ groups.
Also see Appendix B: Sample ERD Exercises
Bibliography
Nguyen Kim Anh, Relational Design Theory. OpenStax CNX. 8 Jul 2009 Retrieved July
2014 from http://cnx.org/contents/606cc532-0b1d-419d-a0ec-ac4e2e2d533b@1@1
Russell, Gordon. Chapter 4 – Normalisation. Database eLearning. N.d. Retrived July
2014 from db.grussell.org/ch4.html
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