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 Post subject: DataBase
PostPosted: Sat Jul 30, 2016 5:51 am 
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Joined: Fri Nov 13, 2015 3:56 am
Posts: 452
Basics of Database
Database:
A database is an organized collection of data.
Database is the collection of schemas, tables, queries, reports, views and other objects.
In one view, databases can be classified according to types of content: bibliographic, full-text, numeric, and images.
A database is a collection of Tables, Schemas, Buffer pools, Logs, Storage groups and Table spaces working together to handle database operations efficiently.
To access information from a database, you need a DBMS. This is a collection of programs that enables you to enter, organize, and select data in a database.
You can create a database in instance using the “CREATE DATABASE” command.

DataBase Management System(DBMS):
A database management system (DBMS) is a computer software application that interacts with the user, other applications, and the database itself to capture and analyze data.
A database management system (DBMS) is a collection of programs that manages the database structure and controls access to the data stored in the database.
DBMSs include MySQL, PostgreSQL,Microsoft SQL Server, Oracle, Sybase and IBM DB2.
Sometimes a DBMS is loosely referred to as a database.
The DBMS serves as the intermediary between the user and the database.
Relational DataBase Management System(RDBMS):
RDBMS is the basis for SQL, and for all modern database systems like MS SQL Server, IBM DB2, Oracle, MySQL, and Microsoft Access.
It is based on the relational model as invented by E.F.Codd.
Relational databases have often replaced legacy hierarchical databases and network databases because they are easier to understand and use

Levels of Database:
The external level defines how each group of end-users sees the organization of data in the database. A single database can have any number of views at the external level.
The conceptual level unifies the various external views into a compatible global view.It provides the synthesis of all the external views.
The internal level or physical level is the internal organization of data inside a DBMS. It is concerned with cost, performance, scalability and other operational matters.

Languages:
Data definition language – defines data types and the relationships among them
Data manipulation language – performs tasks such as inserting, updating, or deleting data occurrences
Query language – allows searching for information and computing derived information

Applications:
Support internal operations of organizations.
It is used to hold more specialized information.
Examples:
Computerized Library System
Telephone directories
Online Reservation System
School registers

Advantages:
Improved data sharing.
Integrity can be enforced
Minimized data inconsistency.
Providing Backup and Recovery
Improved data security.
Concurrency Control
Data Atomicity
Controlling Redundancy
Cost of developing and maintaining system is lower
Data Independence
Support Transactions
Improved decision making

Disadvantages:
Cost of Staff Training is high
Cost of Hardware and Software
Damage occur in Database
It is only efficient for particularly large organizations.
Occupy more size
Database systems are complex (due to data independence), difficult, and time-consuming to design.

Database Administrator(DBA):
A DBA is responsible for keeping the database alive and healthy.It use specialized software to store and organize data.
DBA is Individual responsible for the maintenance and operation of databases.
The role may include capacity planning, installation, configuration, database design, migration, performance monitoring, security, troubleshooting, as well as backup and data recovery.
Database administration is an important function in any organization that is dependent on one or more databases.
The DBA makes sure that the database is protected and that any chance of data loss is minimized.

Database schema in DBMS
A database schema is the skeleton structure that represents the logical view of the entire database. It defines how the data is organized and how the relations among them are associated. It formulates all the constraints that are to be applied on the data.
Schema means a representation of a plan or theory in the form of an outline or model.so with reference to database schema, it means outline of the database you are creating
It’s the database designers who design the schema to help programmers understand the database and make it useful.

A database schema can be divided broadly into two categories −

Physical Database Schema − This schema pertains to the actual storage of data and its form of storage like files, indices, etc. It defines how the data will be stored in a secondary storage.

Logical Database Schema − This schema defines all the logical constraints that need to be applied on the data stored. It defines tables, views, and integrity constraints.

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