Basics of Database Management System (by Yaju Gupta)

Contents

1. Data and Database
2. Database Schema and Instance of DB
3. Data View & Data Independence
4. Data base Management System 
5. Purpose of Designing DBMS
6. Evolution of DBMS
7. Database Languages 
8. Database User's & Its Administration
9. Structure of Database System and 
10. Functionality of Various Components
    
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Data & Database : 

Data : Collection of Facts and Statistics together regarding an Object or Case or Scenario.

Information : Meaningful data.

Database : A place of storing or maintaining data.

Statistics : Statistical process output, that deal with finding new things/facts from existing one based on analyzing collections, organizations and presentations.

Database Schema & Instance

DB Schema : Overall structure of database. Defined using Data Definition Language by Database Administrator .

Instance of DB : Database state at a particular time. That can change with time. For Example :- Medical History database.

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Data View : Look and structure at different levels

Physical Level : How it is stored in file on Hard disk (Sequence of Blocks / Bytes).

Logical Level : Overall logical structure of database, defined by administrator using Data Definition Language (DDL).

View or User Level : The format in which user access the data , only of their concern. In terms of Records / Objects / View.

Data Independence : Changes in the schema of database at any level , doesn't affect on the schema of any other level

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Database Management System

Collection of Inter-related data and set of programs which are used to access these data.

Database is a part of DBMS.

Purpose of Designing DBMS
    
To maintain a Information System for an enterprise .

To provide secure and efficient access and management of data, and 

To provide end user with abstract view of data. In other word they don't need to know how to access data and how it is stored internally.

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Evolution of DBMS

To overcome the problems that occurs while maintaining information System (Database) of an Enterprise in terms of collection of Files (File Processing System).
	
Disadvantages of using File Processing System : 

    Data Access Problem
    Data Isolation Problem
    Data Redundancy & Inconsistency Problem
    Data Atomicity (Transaction Management) Problem
    Concurrent Access Anomalies  
    Security Implementation Problem and 
    Data Integrity Maintenance Problem (Domain, Entity, Validity and Referential Integrity)
           
File Processing System :

In FPS all the data related to an organization / enterprise are stored in different files based on format of data. To access different types of data from different files, there is a need of separate data access programs. As the size of data increases (In parallel additional data access programs are required) their management becomes difficult.

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Database Languages : The languages which are used to access and manipulate data of database ( Database Interaction languages )

For Example : SQL ( Structured Query Language ), QUEL, Data log and QBE (Query by Example)

Different Types of Database Languages

Query Lang. : Used to retrieve information from database

Data Definition Lang. : Used to define logical structure of database (DDL)

Data Manipulation Lang. : Used to update data in database (DML: Procedural and Non Procedural)

Data Control Lang. : Used for Transaction Management (DCL)

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Database User's : Based on the way of interaction with database, all users are classified into following four categories: 

Application User :  Through an Application
Sophisticated User : Direct using Query Language
Naive User : Through Predefined Application 
Database Administrator : Through DDL 

Database Administration : To control the access of data and the programs to access data by different type of users.

Functions of DB Administrator :
    Define & Change DB Logical Structure

    Describe & Change Storage structure of data

    Creation of Data access programs

    Granting authorization to user to access data

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Structure of DBMS



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Components of DBMS 

Query Processor Components

Storage Manager Components ( Operating System Functionality )

Disk Storage ( Where actual data and data access programs are stored )

Query Processor Components : DML Compiler , Embedded Pre DML Compiler , DDL Interpreter and Query Engine .

Storage Manager Components : Buffer Manager , File Manager , Transaction Manager and Authorization and Integrity Manager .

Disk Storage Contents : Data , Indices , Data Dictionary and Statistical Data .

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Functionality of Various Components :

Query Processor Components : 

Embedded Pre DML Compiler : To compile DML statements in Host Language Procedure Call .
DML Compiler : To break a DML statement into small lower level instructions to be executed by Query Engine.
DDL Interpreter : To break DDL statements into small lower level instructions .     
Query Engine : It execute lower level instructions by interacting on with various storage manager components depending on the task to be performed .     

Storage Manager Components : 
File Manager : Used to allocate space and define the structure of data to be stored on disk.

Buffer Manager : Used to transfer data in between main memory and disk and decide data to be placed on Cache.

Transaction Manager : To ensure proper execution of a Transaction ( Atomicity, Consistency, Isolation and Durability )

Authorization & Integrity Manager : To ensure correctness and completeness of data. And also to check that it can be accessed only by authorized user's.    

Disk Storage Contents : 

Data : Collection of Facts related to an Enterprise / Organization .

Statistical Data : New data learned from existing data through statistical process ( Analysis of Collections , Organizations and Presentation of existing data sets ) . Used by DML Compiler for Query Optimization .

Indices : Maintain for fast access of data, or to make search fast for required data .

Data Dictionary : Hold the overall logical structure of database which is defined by database administrator using DDL .

Credits: Yajuvendra Gupta

Tags: Technology,Database,