Important Points Notes of DBMS

Welcome to my new blog post , in this post we will revise or we can say that short notes of DBMS which can be useful to your upcoming examination.so, let's start this,

Data:
 Data means know facts that can be recorded and that have implicit meaning.

Database:

Database is a type of file in which we can store data in systematic way.it makes data management easy.

What is DBMS?

DBMS stands for database management system. it is a collection of inter-related data and set of programs to store and excess those data in an easy and effective manner.

In other words, DBMS is the software which is used to manage the database. For example- MySQL Oracle etc. are a very popular commercial database which is used in different applications.

What is the advantage of DBMS? 

• Controls database redundancy- It can control data redundancy because it stores all the data in one single database file and that recorded data is placed in the database.
• Data Sharing - In DBMS, the authorized users of an organization can share the data among multiple users.
• Easily Maintenance - It can be easily maintainable due to the centralized nature of the database system.
• Reduce Time - It reduce development time and maintenance speed.
• Backup - It provides backup and recovery subsystems which create automatic backup of data from hardware and software failures and restores the data if required.
• Multiple User interface - It provides us different types of user interfaces, like graphical user interface, application program interfaces. 

    OR 

• Redundancy is controlled.
•  Unauthorized access is restricted.
• Providing multiple user interface.
• Enforcing Integrity Constraints.
• Providing backup and recovery. 

What is the disadvantage of DBMS? 

• Cost of Hardware and Software - It requires a high speed of data processor and large memory size to run DBMS software.
• Size - It occupies a large space of disks an large memory to run them efficiently.
• Complexity- Database System creates additional complexity and requirements.
• Higher impact of failure- Failure is highly impacted the database because in most of the organization all the data stored in a single database and if the database is damaged due to electric failure or database corruption then the data may be lost forever.

What is the disadvantage of File Processing System (FCS )?

• Data redundancy and inconsistency.
• Difficult in accessing data.
• Data isolation.
• Data integrity.
• Concurrent access is not possible.
• Security Problems.

ACID PROPERTIES:

DBMS follows the concepts of Atomicity, Consistency, Isolation, and Durability. These concepts are applied on transactions which manipulate data in a database. Acid properties help the database stay healthy in multi-transactional environments and in case of failure.

• ATOMICITY - It says transaction must be treated as atomic.  Either all operations of transactions are properly executed in the database or none.
• CONSISTENCY - The database must remains in a consistent state after any transaction. If any change is made in the database then it should remain preserved always.
• ISOLATION  -  Although multiple transactions may execute concurrently, each transaction must be unware of other concurrently executing transactions.
• DURABILITY - After a transaction completes successfully, the changes it has made to the database persist, even if there are system failures.

                OR

• Atomicity - It entire transaction takes place at once or doesn't happen at all.
• Consistency - The database must be consistent before and after the transaction.
• Isolation - Multiple transactions occur independently without interference.
• Durability - The changes of a successful transaction occurs even if the system failure occurs.

Database Abstraction : 
As database systems are made up of complex data structures. In order to hide this complexity, and ease the interaction between the user and database, the internal irrelevant details are hidden from the users.

This process of hiding the internal complex details is called DATA ABSTRACTION.

There are three levels of data abstraction:

1. Physical level : The lowest level of abstraction describes how data are stored.
2. Logical level : The next higher level of abstraction, describes what data are stored in database and what relationship among those data.
3. View level : The highest level of abstraction describes only part of entire database. It is only part of actual database is viewed by the users.

Data Independence - It refers of being able to modify the schema and one level of database without altering the schema at next higher level.

DBMS ARCHITECTURE:

The design of DBMS depends on its architecture . It can be centralized or decentralized or hierarchical.

There are three types of architecture:

1. 1 - tier architecture(Single Tier Architecture): All the Components (Client, server, and database ) of DBMS reside on a single machine.
2. 2 - tier architecture ( Two Tier Architecture ) : Follows client-server architecture where the server provides DBMS functionality that the client accesses using APIs.
3. 3-tier architecture (Three Tier Architecture ): It consists of application layer in addition to Client and server to provide load balancing and enhance DBMS security.

Three Schema Architecture:

This framework is used to describe the structure of specific database system. It is also called ANSI/SPARC architecture, or 3-level architecture.

• Internal Level - Describes physical storage structure of the database. It defines that how the data will be stored in the block.
• Conceptual Level - Describes structure of the whole database for the complete community of users. It also describes what data are to be stored in the database, and also describes what relationship exist among those data.
• External Level - Describes part of the database of interest to a particular user group. It also describes the different view of database.

Data Model Schema : 

Database schema is the skeleton structure that represents the logical view of entire database. It defines how the data is organize and how the relations among them are associated.

• It defines its entities and relationships among them.
• The database designers design the schema to help programmers to understand the database and make it useful.
• A schema contains objects like table foreign key, primary key, views, columns, data types, stored procedures.
• The process of database creation is called data modeling.

Types of Schema  : 

1. Physical Database Schema: It defines the actual storage of data and its form of storage like files, index etc.
2. Logical Database Schema : It defines all the logical constraints (condition ) that need to be applied on the data stored. It defines tables, views and integrity constants.

Instances :  

The data which is stored in the database at a particular moment of time is called an instance of database.

Database Language : 

A DBMS has appropriate  language and interfaces to express database queries.

Database language can be use to read, store and update the data in the database.

1. DDL ( Data Definition Language ) :- It is used to define database structure. It is used to create schema table, index, constraints etc. in the database. It is used to store the information of meta; Data like no. of table and schema, names, columns in each table, constraints etc.
2. Data Manipulate Language (DML ):-  It is used for accessing and manipulating data in the database, It handles user  request.
3. Data Control Language (DCL ):- It is used to retrieve the stored or save data.
4. Transaction Control Language (TCL ):- It is used to run the changes made by DML statements.