1. Normalization Rules for Database Tables
Normalization Rules for Database Tables
Northern Arizona University
College of Business Administration

2. Normalization - Some Definitions
Normalization - Some Definitions
a relation is a two-dimensional array with a single-valued entry in each cell which has no duplicate rows and has columns whose meaning is the same across all rows.
All tables used in the relational model must be relations.
Normalization is a process for evaluating table structure and reorganizing them as needed to product a set of stable, well-structured relations.
An anomaly is a condition which interferes with the storage, or retention of data or creates the potential for inconsistent data.
There are insertion, modification, and deletion anomalies.
The Normalization process should eliminate anomalies.

3. Unnormalized Tables
An Unnormalized table is a table that does not meet the definition of a relation.
it contains rows with multiple values for an attribute (repeating groups) or
contains duplicate rows.
A table is said to be in first normal form if it meets the definition of a relation
Generally this means it contains no repeating groups of attributes.
The next slide shows an example of an unnormalized table.

4. EMPLOYEE
This EMPLOYEE table is unnormalized - It has cells that do
not contain single-valued entries.
As shown this table has no logical primary key. The E ID# does
not functionally determine the value of Skill.

5. EMPLOYEE
The above employee table shows the same set of data as the
previous slide. It has been reorganized into a form that could
be implemented under some file processing systems, using
COBOL, for instance.
However, it is still not in a form that can be used by the relational
model. The Skills are a multi-valued (repeating group) of
attributes which cannot be identified by the primary key.

6. Eliminating Repeating Groups
Original Table
EMPLOYEE
In most cases, Unnormalized tables can be converted to Sets of Tables that are in at least First Normal form by:
placing any repeating groups of fields in a separate table which includes the primary key attribute from the original table along with a single occurrence of the repeating attribute (Skill in our example).
A Table is in first normal form if it contains no multi-valued attributes

7. Eliminating Repeating Groups
EMPLOYEE
Original
Normalized
EMPLOYEE_SKILL
EMPLOYEE

8. Logical ER Diagram in ER Studio Notation
1st Normal Form Example

9. This Table is in First Normal Form
This Table is in First Normal Form
Schedule of Classes
There are no repeating groups of attributes.
NOTE:
The primary key of this table is a Concatenated key - no single attribute
uniquely identifies a row of the table, but the Combination of Course #
and Section # does uniquely identify a row.
If I know that the Course is CIS 120 and the Section is section 1, I can
identify a unique schedule occurrence.

10. Although this Table is in First Normal Form, it Contains Anomalies
Although this Table is in First Normal Form, it Contains Anomalies
Schedule of Classes
If the description of CIS220 Changes from VB Prog. to Visual C#, I must record the new value in two places (as shown)
- This is a modification anomaly

11. Although this Table is in First Normal Form, it Contains Anomalies
Although this Table is in First Normal Form, it Contains Anomalies ?
Schedule of Classes
If a new course has been designed and I know its description and credit hours
(ACC 266, Pers. Acc., 2 hrs), I still cannot record this data until at least one
section of the course is offered - an insertion anomaly.

12. A Table in First Normal Form Containing Anomalies
A Table in First Normal Form Containing Anomalies
Schedule of Classes
If no section of ACC 255 is offered this semester, I will lose the information
about the description and credit hours of this course. - A deletion anomaly

13. Schedule of Classes
This table has anomalies because it contains partial dependencies.
A partial dependency occurs when one or more attributes in a table depends upon (is functionally determined by) only a portion of a concatenated primary key.
In this case the Description and Cr. Hrs. attributes depend only on Course #. To correct this problem, those attributes determined by only a part of the key should be placed in a separate table. Its Primary key will be the portion of the original primary key required to identify them.

14. Schedule of Classes Original Revised Schedule of Classes COURSE
Notice how this structure eliminates the anomalies we found

15. Logical ER Diagram in ER Studio Notation
2nd Normal Form Example

16. Second Normal Form
Partial Dependencies occur when nonkey attributes are functionally determined by only a portion of a concatenated primary key.
Partial dependencies can occur only in tables with a concatenated key.
Partial dependencies can be corrected by removing those attributes to a separate table whose primary key is just the portion of the key from the original table needed to functionally determine them.
A table is in second Normal Form if it is in first normal form and it contains no partial dependencies.

17. A Table in Second Normal Form Which Has Anomalies
PROFESSOR
This table is in 2nd normal form since it has no repeating groups of attributes
(first normal form) and its primary key is not concatenated.
However, the table above still has anomalies.

18. Anomalies in the Example Professor Table
PROFESSOR
Modification Anomalies -if the Dept Aide serving the ECO department
changes, or if the Fax # of the ECO department changes, this change
would need to be made in several records.
Insertion Anomalies - I want to start a new department and have a Dept Code,
a Dept Aide, and a Dept Fax # (e.g., MKT, T. Taylor, ).
I can’t add this data to the table until at least one professor is hired to teach in
this new department.

19. Anomalies in the Example Professor Table
PROFESSOR
Deletion Anomalies - If Prof # L29 (the only professor in the CIS department in our example table) is deleted, we would lose the information about the name of the Dept Aide for CIS and the Dept Fax # for CIS.

20. This Professor Table has Transitive Dependencies
PROFESSOR
The anomalies we have found occur because the Professor table has transitive dependencies.
Dept Code, Dept Aide, and Dept Fax # are all attributes of a DEPARTMENT entity which is uniquely identified by Dept Code - If I know Dept Code I can uniquely identify Dept Aide and Dept Fax #.
Knowing Prof # allows me to identify these attributes, but only through a chain of inferences - Prof # uniquely identifies Dept Code which, in turn uniquely identifies the other DEPARTMENT attributes.
The anomalies can be resolved by removing the attributes determined by a non-key attribute to a separate table.

21. Correcting Transitive Dependencies
PROFESSOR
Original
Revised
PROFESSOR
DEPARTMENT

22. Logical ER Diagram in ER Studio Notation
3rf Normal Form Example

23. Third Normal Form
Transitive dependencies occur when non-key attributes are functionally determined by other non-key attributes.
Transitive dependencies can be corrected by removing the attributes to a separate table whose primary key is the attribute of the original table which functionally determines them.
The functionally determining attribute serves as a foreign key in the original table.
A table is in Third Normal Form if it is in second normal form and it contains no transitive dependencies.

24. A Proposed Normalization Process for Database Designers
A Proposed Normalization Process for Database Designers
Examine each table of the proposed structure and perform the following operations:
Remove any repeating groups of attributes (multi-valued attributes) to a separate table. If there are independent sets of multi-valued attributes place each set in a separate table.
Remove any attributes that are functionally determined by only a portion of a concatenated key to a separate table.
Remove any attributes that are functionally determined by a non-key attribute to a separate table.

25. Review Question: What Normalization rule(s) are violated by the table below? How would you revise the table Structure?
Write out your answer on a piece of scratch paper.

26. Review Question Solution:
Review Question Solution:
This table violates both 2nd & 3rd normal forms.
Emp. Name and Emp. Class both depend only on Emp No. Which is part of the concatenated key - violates 2nd normal form.
Wage Rate is actually determined by Emp Class a non-key attribute which violates 3rd normal form.
Original Table:
Normalized Tables
Employee Class
Employee Hours
Employee

27. Logical ER Diagram in ER Studio Notation
Review Question Example

28. Merging Relations
View Integration–Combining entities from multiple ER models into common relations
Issues to watch out for when merging entities from different ER models:
Synonyms–two or more attributes with different names but same meaning
Homonyms–attributes with same name but different meanings
Transitive dependencies–even if relations are in 3NF prior to merging, they may not be after merging
Supertype/subtype relationships–may be hidden prior to merging

29. Enterprise Keys
Primary keys that are unique in the whole database, not just within a single relation
Corresponds with the concept of an object ID in object-oriented systems

30. Figure 4-31 Enterprise keys
a) Relations with enterprise key
b) Sample data with enterprise key

31. Mapping Unary Relationships
One-to-Many–Recursive foreign key in the same relation
Many-to-Many–Two relations:
One for the entity type
One for an associative relation in which the primary key has two attributes, both taken from the primary key of the entity

32. Figure 4-17 Mapping a unary 1:N relationship
(a) EMPLOYEE entity with unary relationship
(b) EMPLOYEE relation with recursive foreign key
ER Studio
Notation

33. Figure 4-17 Mapping a unary 1:N relationship
(a) EMPLOYEE entity with unary relationship
(b) EMPLOYEE relation with recursive foreign key

34. Figure 4-18 Mapping a unary M:N relationship
(a) Bill-of-materials relationships (M:N)
(b) ITEM and COMPONENT relations
ER Studio Notation with Sample data
ITEM
COMPONENT
ItemNo
ItemDescrip
ComponentNo
Quantity
ADC8
Audio Card
PCD2 1
MBD2
Motherboard
PC Dual Core
RAM9 4
PCQ5
PC Quad Core
. . .
1GB RAM Chip 8

35. Figure 4-18 Mapping a unary M:N relationship
(a) Bill-of-materials relationships (M:N)
(b) ITEM and COMPONENT relations