1. DBS201: Introduction to Normalization

2. Agenda Top Down vs Bottom Up What is Normalization? Why Normalization?
Normalization Steps

3. Top Down vs Bottom Up Top Down
Usually provided just a narrative or very high level data requirements
Need to discover entities, attributes, relationships
Result is tables

4. Top Down vs Bottom Up Bottom Up Provided with views of data
Views can be screen shots or reports (printouts)
Views contain fields (data)
Need to groups fields together – find fields that are in common
Result is tables

5. Agenda Top Down vs Bottom Up What is Normalization? Why Normalization?
Normalization Steps

6. What is normalization? Normalization
Process for evaluating and correcting table structures to minimize data redundancies
helps eliminate data anomalies
Can be used in conjunction with ER modeling to produce a good database design

7. What is normalization?
Works through a series of stages called normal forms:
Normal form (1NF)
Second normal form (2NF)
Third normal form (3NF)

8. What is normalization? 2NF is better than 1NF 3NF is better than 2NF
For most business database design purposes, 3NF is highest we need to go in the normalization process
Highest level of normalization is not always most desirable

9. Agenda Top Down vs Bottom Up What is Normalization? Why Normalization?
Normalization Steps

10. Why normalization? Example: company that manages building projects
Charges its clients by billing hours spent on each contract
Hourly billing rate is dependent on employee’s position
Periodically, a report is generated that contains information displayed as in Table 5.1

11. A Sample Report Layout

12. A Table in the Report Format

13. Why normalization?
Structure of data set in Figure 5.1 does not handle data very well
The table structure appears to work; report is generated with ease
Unfortunately, the report may yield different results, depending on what data anomaly has occurred

14. Agenda Top Down vs Bottom Up What is Normalization? Why Normalization?
Normalization Steps

15. Conversion to First Normal Form
Relational table must not contain repeating groups
Repeating group
Derives its name from the fact that a group of multiple (related) entries can exist for any single key attribute occurrence
Normalizing the table structure will reduce these data redundancies
Normalization is three-step procedure

16. Step 1: Eliminate the Repeating Groups
Present data in a tabular format, where each cell has a single value and there are no repeating groups
Eliminate repeating groups by eliminating nulls, making sure that each repeating group attribute contains an appropriate data value

17. First Normal Form

18. Step 2: Identify the Primary Key
Primary key must uniquely identify attribute values (a row)
Primary key is PROJ_NUM, EMP_NUM (because the combination of those two uniquely identifies each row of the table)

19. Step 3: Identify all Dependencies
Dependencies can be depicted with the help of a diagram
Dependency diagram:
Depicts all dependencies found within a given table structure
Helpful in getting bird’s-eye view of all relationships among a table’s attributes
Use makes it much less likely that an important dependency will be overlooked

20. Dependency Diagram 1NF PROJ_NUM PROJ_NAME EMP_NUM EMP_NAME JOB_CLASS
CHG_HOUR
HOURS

21. First Normal Form Tabular format in which:
All key attributes are defined
There are no repeating groups in the table
All attributes are dependent on primary key
All relational tables satisfy 1NF requirements
Some tables contain partial dependencies
Dependencies based on only part of the primary key
Still subject to data redundancies
EMPLOYEE_PROJECT(PROJ_NUM(PK), EMP_NUM(PK), PROJ_NAME, EMP_NAME, JOB_CLASS, CHG_HOUR, HOURS)

22. Conversion to Second Normal Form
Relational database design can be improved by converting the database into second normal form (2NF)
Two steps

23. Step 1: Identify All Key Components
Determine which attributes are dependent on which other attributes
Using the dependency diagram, document the partial dependencies: in other words take each part of the primary key and document which attributes are dependent on each part of the primary key

24. Dependency Diagram 2NF 1NF PROJ_NUM PROJ_NAME EMP_NUM EMP_NAME
JOB_CLASS
CHG_HOUR
HOURS

25. Step 2: Identify the Dependent Attributes
Write each key component on separate line, and then write the original (composite) key on the last line
Each component will become the key in a new table
PROJECT (PROJ_NUM (PK), PROJ_NAME)
EMPLOYEE (EMP_NUM(PK), EMP_NAME, JOB_CLASS, CHG_HOUR)
EMPLOYEE_PROJECT(PROJ_NUM(PK), EMP_NUM(PK), HOURS)

26. Second Normal Form Table is in second normal form (2NF) if:
It is in 1NF and
It includes no partial dependencies:
No attribute is dependent on only a portion of the primary key

27. Conversion to Third Normal Form
Data anomalies created are easily eliminated by completing these steps

28. Step 1: Identify Each New Determinant
For every transitive dependency, write its determinant as a PK for a new table
Determinant
Any attribute whose value determines other values within a row
Using the dependency diagram, document the transitive dependencies: in other words identify the attributes dependent on each determinant identified above and identify the dependency

29. Dependency Diagram 3 NF 2NF 1NF PROJ_NUM PROJ_NAME EMP_NUM EMP_NAME
JOB_CLASS
CHG_HOUR
HOURS
JOB_CLASS is a determinant because it can determine other values within the row. In this case, it’s the CHG_HOUR

30. Step 2: Name the table
Name the table to reflect its contents and function
PROJECT (PROJ_NUM (PK), PROJ_NAME)
EMPLOYEE (EMP_NUM(PK), EMP_NAME)
JOB (JOB_CLASS(PK), CHG_HOUR)
EMPLOYEE_PROJECT(PROJ_NUM(PK), EMP_NUM(PK), HOURS)

31. Third Normal Form A table is in third normal form (3NF) if:
It is in 2NF and
It contains no transitive dependencies

32. Improving the Design
Table structures are cleaned up to eliminate the troublesome initial partial and transitive dependencies
Normalization cannot, by itself, be relied on to make good designs
It is valuable because its use helps eliminate data redundancies

33. Improving the Design (continued)
The following changes should be made:
PK assignment
Naming conventions
Attribute atomicity
Adding attributes
Adding relationships (will define the FKs)
Refining PKs
Eliminate derived attributes

34. Business Rules Business Rules drive the relationships
Look at the data in the table and understand/interpret what the relationship is between the data

35. Business Rules
A job class can have more than 1 employee in it; results in a 1:M relationships between JOB and EMPLOYEE
Add the FKs into the appropriate tables

36. Step 2: Name the table
Name the table to reflect its contents and function
PROJECT (PROJ_NUM (PK), PROJ_NAME)
EMPLOYEE (EMP_NUM(PK), EMP_NAME, JOB_CLASS(FK))
JOB (JOB_CLASS(PK), CHG_HOUR)
EMPLOYEE_PROJECT(PROJ_NUM(PK), EMP_NUM(PK), HOURS)
New foreign key
Business rule not necessary between EMPLOYEE and PROJECT. Why?

37. First Normal Form

38. Normalization and Database Design
Normalization should be part of design process
Make sure that proposed entities meet required normal form before table structures are created
ER diagram
Provides the big picture, or macro view, of an organization’s data requirements and operations
Created through an iterative process
Identifying relevant entities, their attributes and their relationship
Use results to identify additional entities and attributes

39. ERD

40. Normalization and Database Design (continued)
Normalization procedures
Focus on the characteristics of specific entities
A micro view of the entities within the ER diagram
Difficult to separate normalization process from ER modeling process
Two techniques should be used concurrently

41. Summary
Normalization is a table design technique aimed at minimizing data redundancies
First three normal forms (1NF, 2NF, and 3NF) are most commonly encountered
Normalization is an important part—but only a part—of the design process
Continue the iterative ER process until all entities and their attributes are defined and all equivalent tables are in 3NF

42. Normalization Exercise
STU_NUM
STU_LNAME
STU_MAJOR
DEPT_CODE
DEPT_NAME
DEPT_PHONE
211343
Stephanos
Accounting
ACCT
4356
200128
Smth
199876
Jones
Marketing
MKTG
4378
Ortiz
223456
McKulski
Statistics
MATH
Mathematics
3420
Normalize the above table.
1NF – eliminate repeating groups, identify a PK for the table structure
2NF – find partial dependencies
3NF - find transitive dependencies
Write final table structures, including all relationships. Make all attributes atomic.

43. Normalization Exercise
Vehicle Num
Model
Year
Acme Tire Number
Tire Manfctr
Size
KM This Vehicle 11
Ford
1997
1327
Goodyear
15R7
43000
1328
1329
25000
1330
24000 15
Chevrolet
1999
2013
BF Goodrich
18000
2014
29000
Normalize the above table.
1NF – eliminate repeating groups, identify a PK for the table structure
2NF – find partial dependencies
3NF - find transitive dependencies
Write final table structures, including all relationships. Make all attributes atomic.