Introduction of DBMS

Data: Facts, figures, statistics etc.

Record: Collection of related data items.

Table or Relation: Collection of related records.

Database: Collection of related relation/data. In database, data is organized strictly in row and column format.The columns are called Fields, Attributes or Domains. The rows are called Tuples or Records.

Features of Data In a Database:
1)Security
2)Consistency
3)Non-Redundancy
4)Shared
5)Independence
6)Persistence

DBMS(Database Management System)It is software that allows creation, definition and manipulation of database.l It is middle layer between data and program.

File System:

• Stores permanent records in various files

• Need application program to access and manipulate data.

Disadvantage of File System:

• Data Redundancy
• Data Inconsistency
• Difficult in accessing data
• Data Integrity
• Low Security

Data Abstraction:To simplify the interaction of users and database, DBMS hides some information which is not user interest is called Data Abstraction. So, developer hides complexity from users and show Abstract view of data.

DBMS Architecture/3-Tier Architecture:

1)External/View Level:It is user's view of the database.This level describes the part of the database that is relevant to each user.

2)Conceptual/Logical Level:

• Describes what data is stored in the database and the relationship among the data.
• Represent all entities, their attributes and their relationship
• Constraints on the data
• Security and Integrity information

3)Physical/Internal Level:

• Describes how the data is stored in the database
• Storage Space allocation for data and indexes
• File System
• Data compression and Data encryption techniques
• Record Placement

Schemas: 

• It is overall description of the database.In three-level architecture, one schema at each level.
• Does not specify relationship among files.

Instances:

Collection of information stored in the database at a particular moment.

Sub-schema:It is a subset of schema and inherits the same property that the schema has. It is an application programmer's or user view of the data items types and record types which he or she uses.