1. Week 06 - Normalisation
INFOSYS 222

2. Agenda Agenda Normalisation and normal forms 1NF, 2NF and 3NF
Practice on normalisation with previous exam questions

3. Normalisation What is normalisation? What are 1NF, 2NF and 3NF?
Why do we need normalisation?
What would we achieve at the end of normalisation?
What are 1NF, 2NF and 3NF?
What are functional dependencies?
What are partial functional dependencies?
What are transitive functional dependencies

4. Normalisation
Normalisation is a process that “improves” a database design by generating relations that are of higher normal forms.
The objective of normalisation:
“to create relations where every dependency is on the key, the whole key, and nothing but the key”.
Minimize information duplication

5. Work Allocation Chart emp_No emp_Name rank_Id rank_Desc salary
project_No
project_Desc
project_Start_Date
123
John 01
Sr.Engr
52K
ABC34
Waste disposal
01/03/15
456
Alan 03
App. Spec
35K
QXN88
Sludge treatment
20/06/15
555
Peter 02
Engr
40K
12/03/15
467
Jane
BAT20
N2O Generation
09/05/15
15/06/15
03/05/15
Show how to write 1NF

6. Functional dependencies
We say an attribute, B, has a functional dependency on another attribute, A, if for any two records, which have
the same value for A, then the values for B in these two records must be the same. We illustrate this as:
A  B
Example: We only track one name for each employee. Suppose each employee is identified by their unique employee number. We say there is a functional dependency of name on employee number:
employee number  employee name

7. Functional dependencies
If emp_No is the PK then the FDs:
emp_No  emp_Name
emp_No  rank_Desc
emp_No  salary
must exist.
emp_No is not the PK : A row is not unique
emp_No and project_No : is unique
Show 1NF with keys underlined

8. Partial dependency
A partial dependency exists when an attribute B is functionally dependent on an attribute A, and A is a component of a multipart candidate key.
emp_No
project_No
project_StartDate
project_Desc
Candidate keys: {emp_No, project_No}
project_Desc is partially dependent on {emp_No, project_No} as
project_No is a determinant of project_Desc and project_No is part of a candidate key
Show that partial dependencies are removed to a separate relation
Relations in 2NF

9. Transitive dependency
Consider attributes A, B, and C, and where
A  B and B  C.
Functional dependencies are transitive, which means that we also have the functional dependency A  C
We say that C is transitively dependent on A through B.
For non key attributes

10. Transitive dependency
emp_No  rank_Id
emp_No emp_Name rank_Id rank_Desc
rank_Id  rank_Desc
emp_No emp_Name rank_Id rank_Desc
Remove all transitive dependent attributes together with their determinant to a new relation
Show 3NF relations
rank_Desc is transitively dependent on emp_No via rank_Id
emp_No  rank_Desc

11. INFOSYS 222 AC 2007 Exam
101
Derive a set of relation in 3NF. Show each step of normalisation clearly. All PKs should have a solid underline and FKs a dashed line. Draw an ERD for the derived relations

12. INFOSYS 222 AC 2016 Exam

13. INFOSYS 222 AC 2016 Exam
Derive a set of relations in third normal form (3NF), using the data shown in figure above
Clearly show each step of normalisation – 1NF, 2NF and 3NF