Wednesday, November 25, 2015

Database Management System (DBMS) For IBPS IT Officer

DBMS is a topic which is normally weighted 10-20 marks out of 75 marks in professional knowledge section. So read properly.

What is DBMS or DBS(Database System)?

DBMS consist of
i) Database(DB): a logically coherent collection of interrelated and persistent data.
II) A set of programs used to access, update and manage data, which is called Database Management System.

DBMS is a collection of programs that enable users to create and maintain a database. DBMS provide an environment which is convenient for storing and retrieving information to and from the database.

Advantages of DBMS

  • Redundancy is controlled
  • Unauthorized access is restricted
  • Providing multiple user interface
  • Enforcing integrity constraints
  • Providing backup and recovery
  • Data sharing
  • Data and program independence
Example of database management: Saving Bank Accounts Data
In banks, the data of SB accounts are maintained in the databases. The data is accessible in various ways means internet banking, mobile banking, Bank's software used at bank counters. Debit and Credit of account balance can be done in all three ways, but the data that got updated is same. we use a different application to manage same data i.e. account balance.

See the above picture for better understand the DBMS and DB. Now that you have already understood what is Database and DBMS, let's move deeper.

Data Model

Data modelling is the first process of database development process. Database designers first create a conceptual model of how data items relate to each other. A data model is a collection of high-level data description that hide many low-level storage details. A data model is a tool for data abstraction, represents the organisation itself and help users clearly communicate their understanding of organizational data. 

Data Abstraction

Main Purpose of the database system is to provide users with an abstract view of the system. The system hides certain details of how data is stored and created and maintained. The complexity of storage should be hidden from the database users.

File Structures

Sequential structures

Major characteristics of this type of file system are:
a.) Records should be accessed in the same order in which they were written. In simple words, there is no way to directly jump to some record by skipping other records.
b.) If anyone record has to be updated, then the whole file has to be rewritten to another file. An example of this type of database is Payroll Book. Here changes in payroll are updated by making a new file every month.

Random Access Structure

Many real world application requires random access to the database. Two main type of random access file structure is 'indexed file' and 'indexed sequential files'. Consider and example of students of the particular class, where students roll number, name, attendance, marks are entered. Now you want to access any particular students data then you need an identifier that is unique to that student. Roll number is a unique identifier that is called record key.  Usually, a file must have one unique key and that is called primary key.  In some complex databases, one key may not be sufficient. For example, if we have a database of the whole school then there will be same roll numbers in different class, and we will need to use two keys like Class Name & Roll Number. A key thus formed by joining two keys is called Concatenated Key. As this combination uniquely identifies the record concatenated key can be used as a primary key. All other fields which do not uniquely identify the record are called Secondary Keys. 

Understand the Keys concept properly there can be some questions from them. 

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