Computer-2

Let’s discuss about various concepts of DBMS today.

It stands for Data Base Management System.

Data base is collection of data like tables.

The software that is used to regulate database is called DBMS.

Now ... DBMS is of different types like Hierarchical.... Relational etc.

In case of hierarchical DBMS.... data is stored in form of trees.

While in case of Relational DBMS ... data is stored in form of tables.

One of the most popular Relational Database Management Systems (RDBMS) is Oracle.  

There is one term called Data Redundancy means Duplication of data.

In DBMS, sometimes a term is used known as data-abstraction means hiding certain details of database from users.

E.g. We listen to headlines of news that is an abstract view of news but when we listen to news properly then whole news are understood.

Let’s know about few terms: Entity and Attribute

An entity is simply an object (like a table in RDBMS).

Examples are many like in case of database of an organisation entities can be Employees etc.

Let’s understand about Attribute.

It’s basically properties of an entity.

Example: Employees entity can have many Attributes like Salary, Employee – id etc.

Generally ... comprehensive questions about DBMS are asked in IBPS-IT officer exam. In IBPS clerk exam it’s expected that deep questions would not be asked.

Do you know what’s difference between Superkey, Candidate key, Primary key and Foreign key?

Superkey: It’s name of a unique attribute or unique combination of attributes.

Let’s take an example:

Two employees may have same name like Sahil.  

Now ... cast may also be same ...

i.e. Two employees may have same full name :

E.g.: Sahil Gupta

In this case ... we can take set of Name and DOB (Date of Birth)

This set of attributes is called *Super key*

Now ... two employees may have same full name like:

Sahil Gupta (DOB: 29/06/87)

Sahil Gupta (DOB: 24/09/84)

Now ... Let’s understand about Candidate key.

 It’s set of minimal attributes.

We can say that it’s minimal super key.

Thus ... in a database like table we check superkeys first then we find Candidate Key then at last that candidate key is designated as Primary-key.  

In RDBMS ... generally we designate a primary key in a table like in Employees table ...  Employee-id can be designated as Primary key.

There is a foreign-key also which is used in other table to connect with first table in which we designate Primary key.

Like ... in employee table ... employee-id is a primary key.

In Employee address table ... employee-id attribute can be used as foreign key.  

         In further ... lectures ... we will grasp more knowledge...