DBMS Notes I

DBMS
DBMS is a software for managing data for efficient storage and fast retrievals from database.
Database: An organinzed collection of data.

Types of DBMS:

There are 4 types of DBMS:

1. Relational Database Management System (RDBMS) - Data is stored in tables, in form of rows and columns
2. Object Oriented Database Management System - Data is stored as objects, attributes and methods. No table, no rows, no column.
3. Hierarchical Database management system - Data is stored in form of one to many relationships. We can visual it like tree.
4. Network Database management system. Same as Hierarchical DBMS, but one object can have multiple parent.

File System vs DBMS (Disadvanges of File System):

• Data redundancy: Duplicate data
• Data Inconsistency: Problem in updation and access of data
• Data Isolation: Not able to get overview of data.
• No ACID Property
• No Security

DBMS Architecture

There are three types of DBMS architecture:

1. Single tier architecture - Client system communicate directly to DBMS
2. Two tier architecture - Two nodes available 1. Client 2. Server + Database
3. Three tier architecture: Three Nodes: 1. Client 2. Sever 3. Database. Cient communicate to Server and server to Database.

DBMS Three Level Architecture Diagram

This architecture has three levels:

1. External level
   • Highest leve of abstraction
   • Only those portion of the database is available to the user that is concerned to their program or their application
   • User doesn’t need to know the schema details
   • This is also called user level.
   • Describes the user interaction with database system
   • Eg: we can show only the profile details to the logged in user.
2. Conceptual level
   • Also called logical level
   • Maintained by DBA (database administrator)
   • Generally programmers works at this level.
   • Includes all records and relationships
3. Internal level
   • Lowest level of abstraction
   • Also known as physical level
   • Describes how the data is actually stored in the storage devices
   • It is described as blocks of storage (bytes, gigabytes, terabytes etc.) in memory.
   • Responsible for allocating space to the data
     

Data Abstracation:

• Developers hide internal implemntation and irrelevant details from users for the ease of use.
• Three level architecutre are 3 levels of abstraction.

Schema

• Design of a database is called the schema.
• Types: Physical schema, logical schema and view schema

Instance of a database:

• Snapshot of the database image at a particualar instance of time.

DBMS Languages

1. DDL: It is used for creating tables, schema, indexes, constraints etc.
2. DML: It is used for accessing and manipulating data in a database.
3. DCL: It is used for granting and revoking user access on a database.
4. TCL Transaction control language for management of transaction. Either to commit or rollback.
   

NS: DBMS Complete Notes for interview prep.