• Data
  • A fact which can be stored
• Database
  • A collection of relative data. A logically coherent collection of data with some inherent meaning.
  • It represents some aspect of the real world, called the universe of discourse.
• DBMS
  • A software tool to organize (create, retrieve, update and manage) data in a database. In other words, a set of programs to create and manipulate a database.
  • It is an interface between user and database.
  • It is a software through which we can execute SQL queries.
  • Oracle, MySql, Microsoft SQL servers are popular Database Management Systems.

• Youtube - DBMS tutorials
• http://www.geeksengine.com/database/design/data-integrity.php
• https://www.tutorialcup.com/dbms/constraints.htm

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Database systems are meant to handle a large collection of information. Management of data involves both defining structures for storage of information and providing mechanisms that can do the manipulation of those stored information. Moreover, the database system must ensure the safety of the information stored, despite system crashes or attempts at unauthorized access.

• Data independence - Application programs should be as free or independent as possible from details of data representation and storage. DBMS can supply an abstract view of the data for insulating application code from such facts.
• Efficient data access - DBMS utilizes a mixture of sophisticated concepts and techniques for storing and retrieving data competently and this feature becomes important in cases where the data is stored on external storage devices.
• Data integrity and security - If data is accessed through the DBMS, the DBMS can enforce integrity constraints on the data.
• Data administration - When several users share the data, integrating the administration of data can offer major improvements. Experienced professionals understand the nature of the data being managed and can be responsible for organizing the data representation to reduce redundancy and make the data to retrieve efficiently.

• Defining a database - It involves specifying the structures, the data types, and constraints of the data to be stored in the database.
• Constructing a database - It means storing the data on some storage medium that is controlled by the DBMS.
• Manipulating a database - It includes functions such as retrieving data from the database and updating the database.
• Sharing a database - It allows multiple users and programs to access the database simultaneously.
• Protecting and maintaining a database

A schema can be defined as the design of a database. The overall description of the database is called the database schema. 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 to the data. It contains a descriptive detail of the database, which can be depicted by means of schema diagrams. It is designed when the database doesn't exist at all. A database schema does not contain any data or information.

A database instance is a state of operational database with data at any given time. It contains a snapshot of the database. Database instances tend to change with time. A DBMS ensures that its every instance (state) is in a valid state, by diligently following all the validations, constraints, and conditions that the database designers have imposed.

Contains the complete definition or description of the database structure and constraints. The information stored in the DBMS catalog is called meta-data.

• DDL - The language by which database-schema is defined is called DDL(Data Definition Language). Consistency constraints which should be satisfied by data values stored in the database can be specified by DDL.
• DML - The language by which users manipulate or access data stored in database is called DML(Data Manipulation Language).

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