I. INTRODUCING DATABASES :
Concept of a Database :
Traditional Approach : In this approach, independent application programs access their own independent data files. This results in many problems in data storage and retrieval.
Database Approach : In this approach, all application access a common database, which is a centralized data storage system.
This approach has the following advantages :
Redundancy of data storage is reduced, Inconsistency in data is eliminated & Data sharing between applications is possible.
Interacting with a Database :
Database Management System (DBMS) : DBMS is a software that interfaces between applications and a database for all data processing activities.
Users of a DBMS : End Users, Application Programmers and Database Administrators use a DBMS, either directly or indirectly.
How users interact with a Database :
1. End users send queries to the DBMS through applications.
2. The DBMS translates the queries.
3. The DBMS retrieves data from the database.
4. The DBMS sends data to the application, which present the data to the end users.
Functions of a DBMS :
Function of DBMS Description Provided by using
Defining the data structure Defining structure of data to be stored in database Data Definition Language (DDL)
Manipulating Data Retrieving, adding, modifying, deleting data. Data Manipulation Language (DML)
Data Security Preventing unauthorized access to data. User-ids and Passwords.
Control of Data Access Allowing users to use only relevant data Data Control Language (DCL)
Architecture of a Database :
Need for an Architecture : The details about complexity and structure of data in a database in not required by end-users. Therefore, differentiating what the end-users see and what is actually there in a database is important.
Architecture of a Database : The architecture of a database comprises a set of three levels at which a database can be viewed.
External Level or View, Conceptual Level or View & Internal Level or View.
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