1. Relational Database Management Systems
Objectives
• In this session, you will learn to:
Describe data redundancy
Describe the first, second, and third normal forms
Describe the Boyce-Codd Normal Form
Appreciate the need for denormalization
Ver. 1.0 Session 3 Slide 1 of 15
2. Relational Database Management Systems
Understanding Data Redundancy
Redundancy means repetition of data.
Redundancy increases the time involved in updating,
adding, and deleting data.
It also increases the utilization of disk space and hence,
disk I/O increases.
Redundancy can lead to the following problems:
Inserting, modifying, and deleting data may cause
inconsistencies
Errors are more likely to occur when facts are repeated
Unnecessary utilization of extra disk space
Ver. 1.0 Session 3 Slide 2 of 15
3. Relational Database Management Systems
Definition of Normalization
Normalization is a scientific method of breaking down
complex table structures into simple table structures by
using certain rules.
It allows you to reduce redundancy in a table and eliminate
the problems of inconsistency and disk space usage.
Normalization results in the formation of tables that satisfy
certain specified rules and represent certain normal forms.
The most important and widely used normal forms are:
First Normal Form (1NF)
Second Normal Form (2NF)
Third Normal Form (3NF)
Boyce-Codd Normal Form (BCNF)
Ver. 1.0 Session 3 Slide 3 of 15
4. Relational Database Management Systems
First Normal Form (1 NF)
A table is said to be in the 1NF when each cell of the table
contains precisely one value.
Functional Dependency:
The normalization theory is based on the fundamental notion of
functional dependency.
Given a relation R, attribute A is functionally dependent on
attribute B if each value of A in R is associated with precisely
one value of B.
Ver. 1.0 Session 3 Slide 4 of 15
5. Relational Database Management Systems
Second Normal Form (2 NF)
A table is said to be in 2NF when it is in 1NF and every
attribute in the row is functionally dependent upon the whole
key, and not just part of the key.
To ensure that a table is in 2NF, you should:
Find and remove attributes that are functionally dependent on
only a part of the key and not on the whole key and place them
in a different table.
Group the remaining attributes.
Ver. 1.0 Session 3 Slide 5 of 15
6. Relational Database Management Systems
Third Normal Form (3 NF)
A relation is said to be in 3NF when it is in 2NF and every
non-key attribute is functionally dependent only on the
primary key.
To ensure that a table is in 3NF, you should:
Find and remove non-key attributes that are functionally
dependent on attributes that are not the primary key and place
them in a different table.
Group the remaining attributes.
Ver. 1.0 Session 3 Slide 6 of 15
7. Relational Database Management Systems
Boyce-Codd Normal Form (BCNF)
The original definition of 3NF was inadequate in some
situations.
It was not satisfactory for the tables:
that had multiple candidate keys
where the multiple candidate keys were composite
where the multiple candidate keys overlapped
Therefore, a new normal form-the BCNF was introduced:
A relation is in the BCNF if and only if every determinant is a
candidate key.
Ver. 1.0 Session 3 Slide 7 of 15
8. Relational Database Management Systems
Boyce-Codd Normal Form (BCNF) (Contd.)
In order to ensure that a table is in BCNF, you should:
Find and remove the overlapping candidate keys.
Place the part of the candidate key and the attribute it is
functionally dependent on, in a different table.
Group the remaining items into a table.
Ver. 1.0 Session 3 Slide 8 of 15
9. Relational Database Management Systems
Just a minute
Which of the following help in achieving a good database
design?
1. A table should store data for all the related entities together.
2. Each table should have an identifier.
3. Columns that contain NULL values should be created.
Answer:
2. Each table should have an identifier.
Ver. 1.0 Session 3 Slide 9 of 15
10. Relational Database Management Systems
Just a minute
For which normal form you need to remove non-key
attributes that are functionally dependent on attributes that
are not primary key?
Solution:
Third normal form
Ver. 1.0 Session 3 Slide 10 of 15
11. Relational Database Management Systems
Understanding Denormalization
The end product of normalization is a set of related tables
that comprise the database.
However, in the interests of speed of response to critical
queries, which demand information from more than one
table, it is sometimes wiser to introduce a degree of
redundancy in tables.
The intentional introduction of redundancy in a table to
improve performance is called denormalization.
Ver. 1.0 Session 3 Slide 11 of 15
12. Relational Database Management Systems
Just a minute
In the reporting system, the total amount paid to a
contract recruiter is often required. The required result
can be calculated using the two tables,
ContractRecruiter and Payment.
ContractRecruiter Payment
cContractRecruiterCode cSourceCode
cName mAmount
vAddress cChequeNo
cCity dDate
siPercentageCharge
Since the size of the Payment table is large, the join
between the two tables takes time to generate the
required output. It is, therefore, necessary to improve
the performance of this query.
Ver. 1.0 Session 3 Slide 12 of 15
13. Relational Database Management Systems
Just a minute
Answer:
Denormalize the tables. Add a column called mTotalPaid to
the ContractRecruiter table.
ContractRecruiter
cContractRecruiterCode
cName
vAddress
cCity
siPercentageCharge
mTotalPaid
Ver. 1.0 Session 3 Slide 13 of 15
14. Relational Database Management Systems
Summary
In this session, you learned that:
Normalization is used to simplify table structures.
Normalization results in the formation of tables that satisfy
certain specified constraints, and represent certain normal
forms. The normal forms are used to ensure that various types
of anomalies and inconsistencies are not introduced in the
database. A table structure is always in a certain normal form.
Several normal forms have been identified.
The most important and widely used of these are:
First Normal Form (1NF)
Second Normal Form (2NF)
Third Normal Form (3NF)
Boyce Codd Normal Form (BCNF)
Ver. 1.0 Session 3 Slide 14 of 15
15. Relational Database Management Systems
Summary (Contd.)
The intentional introduction of redundancy in a table in order to
improve performance is called denormalization.
The decision to denormalize results in a trade-off between
performance and data integrity.
Denormalization increases disk space utilization.
Ver. 1.0 Session 3 Slide 15 of 15
Editor's Notes
Students have learnt the structure of different types of dimensions and the importance of surrogate keys in Module I. In this session, students will learn to load the data into the dimension tables after the data has been transformed in the transformation phase. In addition, students will also learn to update data into these dimension tables. Students already know about different types of dimension tables. Therefore, you can start the session by recapitulating the concepts. Initiate the class by asking the following questions: 1. What are the different types of dimensions? 2. Define flat dimension. 3. What are conformed dimension? 4. Define large dimension. 5. Define small dimension. 6. What is the importance of surrogate key in a dimension table? Students will learn the loading and update strategies theoretically in this session. The demonstration to load and update the data in the dimension table will be covered in next session.
Students know the importance of surrogate keys. In this session students will learn the strategy to generate the surrogate key. Give an example to explain the strategy to generate the surrogate keys by concatenating the primary key of the source table with the date stamp. For example, data from a Product table has to be loaded into the Product_Dim dimension table on Feb 09, 2006. The product_code is the primary key column in the Product table. To insert the surrogate key values before loading the data into the dimension table, you can combine the primary key value with the date on which the data has to be loaded. In this case the surrogate key value can be product_code+09022006.
Students have learnt the structure of different types of dimensions and the importance of surrogate keys in Module I. In this session, students will learn to load the data into the dimension tables after the data has been transformed in the transformation phase. In addition, students will also learn to update data into these dimension tables. Students already know about different types of dimension tables. Therefore, you can start the session by recapitulating the concepts. Initiate the class by asking the following questions: 1. What are the different types of dimensions? 2. Define flat dimension. 3. What are conformed dimension? 4. Define large dimension. 5. Define small dimension. 6. What is the importance of surrogate key in a dimension table? Students will learn the loading and update strategies theoretically in this session. The demonstration to load and update the data in the dimension table will be covered in next session.
Explain the strategy to load the data into conformed dimension with help of an example to load the data in the date dimension given in SG. Explain the strategy to load the data into the Snowflaked dimension with the help of an example given in SG.
Explain the strategy to load the data into conformed dimension with help of an example to load the data in the date dimension given in SG. Explain the strategy to load the data into the Snowflaked dimension with the help of an example given in SG.
Explain the strategy to load the data into conformed dimension with help of an example to load the data in the date dimension given in SG. Explain the strategy to load the data into the Snowflaked dimension with the help of an example given in SG.
Explain the strategy to load the data into conformed dimension with help of an example to load the data in the date dimension given in SG. Explain the strategy to load the data into the Snowflaked dimension with the help of an example given in SG.
Explain the strategy to load the data into conformed dimension with help of an example to load the data in the date dimension given in SG. Explain the strategy to load the data into the Snowflaked dimension with the help of an example given in SG.
Student already have learnt about SCDs in Module I. Therefore, you can start this topic by asking the following questions to students: What are type 1 SCDs? Given an example to explain type 1 SCDs. This will recapitulate what they have learnt about type 1 SCD in Module 1. Now explain the strategy to load the data into these dimension tables with help of the given diagram. Relate this diagram to the example given in SG.
You can summarize the session by running through the summary given in SG. In addition, you can also ask students summarize what they have learnt in this session.
You can summarize the session by running through the summary given in SG. In addition, you can also ask students summarize what they have learnt in this session.
