Important Computer Awareness Materials for IBPS Exams 2017 (Day-8)

Important Computer Awareness for IBPS Exams 2017 (Day-8) – DBMS Part-8:
Dear Readers, IBPS Exams are approaching shortly, we all knew that Computer Awareness is one of the important section, which will help you to increase your score easily.

Many of our followers were asking us to provide Important Computer Awareness Notes along with the model questions, here we have planned to provide the Topic wise Important Computer Awareness Materials on Daily basis, and also we will provide MCQs based on these topics daily. Kindly follow us regularly and make use of it.

Database Management Systems (DBMS) – PART 8

Normalization and Anomalies:

Anomalies:
Tables that have redundant data have problems known as anomalies. So data redundancy is cause of an anomaly.
Redundancy is duplication of the data.
Three types of anomalies:
1. Insert Anomaly
2. Update Anomaly
3. Delete Anomaly
1. Insert Anomaly:
When you insert a record without having it stored on the related record.
An Insert Anomaly occurs when certain attributes cannot be inserted into the database without the presence of other attributes. For example this is the converse of delete anomaly – we can’t add a new course unless we have at least one student enrolled on the course.
2. Update Anomaly:
When you delete some information and lose valuable related information at the same time.
An Update Anomaly exists when one or more instances of duplicated data is updated, but not all. For example, consider Jones moving address – you need to update all instances of Jones’s address.
3.  Delete Anomaly:
Any change made to your data will require you to scan all records to make the changes multiple time.
Delete Anomaly exists when certain attributes are lost because of the deletion of other attributes. For example, consider what happens if Student S30 is the last student to leave the course – All information about the course is lost.
Normalization Stages:
Process involves applying a series of tests on a relation to determine whether it satisfies or violates the requirements of a given normal form.
·       When a test fails, the relation is decomposed into simpler relations that individually meet the normalization tests.
·       The higher the normal form the less vulnerable to update anomalies the relations become.
·       Three Normal forms: 1NF, 2NF and 3NF were initially proposed by Codd.
·       All these normal forms are based on the functional dependencies among the attributes of a relation.
Normalization follows a staged process that obeys a set of rules. The steps of normalization are:
Step 1: Select the data source and convert into an unnormalised table (UNF)
Step 2: Transform the unnormalised data into first normal form (1NF)
Step 3: Transform data in first normal form (1NF) into second normal form (2NF)
Step 4: Transform data in second normal form (2NF) into third normal form (3NF)
Occasionally, the data may still be subject to anomalies in third normal form. In this case, we may have to perform further transformations.
·       Transform third normal form to Boyce-Codd normal form (BCNF)
·       Transform Boyce-Codd normal form to fourth normal form (4NF)
·       Transform fourth normal form to fifth normal form (5NF)
1 NF Form:
Each table cell should contain a single value.
Each record needs to be unique.
1 NF Example:
2 NF Form:
Rule 1: Be in 1NF
Rule 2: Single column primary key.
We have divided our 1NF table into two tables as Table 1 and table 2. Whereas table 1 contains member information and table 2 contains information on movies rented.
We have introduced a new column called Membership_id which is the primary key for table 1. Records can be uniquely identified in Table 1 using membership id
3 NF Form:
Step 1:Be in 2NF
Step 2:Has no transitive functional dependencies
To move our 2NF table into 3NF, we again need to need to divide our table.
We have again divided our tables and created a new table which stores Salutations. 
There are no transitive functional dependencies, and hence our table is in 3NF
In Table 3 Salutation ID is primary key, and in Table 1 Salutation ID is foreign to primary key in Table 3

BCNF:

Even when a database is in 3rd Normal Form, still there would be anomalies resulted if it has more than one Candidate Key.
Sometimes is BCNF is also referred as 3.5 Normal Form.

4NF (Fourth Normal Form) Rules:

If no database table instance contains two or more, independent and multivalued data describing the relevant entity, then it is in 4th Normal Form.

5NF (Fifth Normal Form) Rules:

A table is in 5th Normal Form only if it is in 4NF and it cannot be decomposed into any number of smaller tables without loss of data.

6NF (Sixth Normal Form) Proposed:

6th Normal Form is not standardized, yet however, it is being discussed by database experts for some time. Hopefully, we would have a clear& standardized definition for 6th Normal Form in the near future…
That’s all to Normalization!!!
  • David

    Please arrange computer notes and quizes day wise , It’s hard to search