Database
Collection of Data
Management System
a set of programs to store and retrieve data.
DBMS
(Database Management System)
A
... [Show More] collection of inter-related data that contains programs to store & access that data in an easy and effective manner.
What is the need of DBMS?
Store Data in an optimized and systematic manner
and
Retrieve Data Fast
What are some Examples Applications where we use Database Management Systems are:
Telecom
Industry
Banking
Education sector
Online shopping
Advantages of DBMS over a FILE System
no redundant data
Data consistency and Integrity
Secure
Privacy
Easy access to data
Easy recovery
Flexible
Disadvantages of DBMS over FILE System
Higher implementation Cost
Complexity
Performance for some applications
What must you have to understand the view of data?
Data Abstraction
Instance and Schema
What is data abstraction?
The process of hiding irrelevant details from user
What are the 3 levels of Data abstraction?
Physical
Logical
View
Physical abstraction level
This is the lowest level of data abstraction. It describes how data is actually stored in database. You can get the complex data structure details at this level.
records can be described as blocks of storage (bytes, gigabytes, terabytes etc.) in memory.
Logical abstraction level
- Middle level
- Describes what data is stored in database
- Developers and admins access this level.
- records can be described as fields and attributes along with their data types, their relationship among each other can be logically implemented.
View abstraction level
- Highest level of data abstraction.
- Describes the user interaction with database system.
user just interact with system with the help of GUI and enter the details at the screen, they are not aware of how the data is stored and what data is stored; such details are hidden from them.
Database Instance
The data stored in database at a particular moment of time
Database vs Instance
Database is the set of files where application data (the reason for a database) and meta data is stored.
An instance is the software (and memory) that Oracle uses to manipulate the data in the database.
Database Schema
Design of a database.
Defines the variable declarations in tables that belong to a particular database;
3 Schema levels
Physical
Logical
View
keys in DBMS
Used for identifying unique rows from table.
Establishes relationship among tables.
Types of keys
Primary
Super
Candidate
Alternate
Composite
Foreign [Show Less]