Database Management System : Database Management System An Introduction
What is Data ? : What is Data ? Data (singular: datum) are collection of natural phenomena descriptors including the results of experience, observation or experiment, or a set of premises/environment. This may consist of numbers, words, or images, particularly as measurements or observations of a set of variables.
Raw data are numbers, characters, images or other outputs from devices to convert physical quantities into symbols. Such data are typically further processed by a human or input into a computer, stored and processed there, or transmitted (output) to another human or computer.
What is Database (DB) ? : What is Database (DB) ? A database is a structured collection of records or data. A computer database relies upon software to organize the storage of data. It can also be thought of as a collection of information that is organized so that it can easily be accessed, managed, and updated.
Computer databases typically contain aggregations of data records or files, such as sales transactions, product catalogs and inventories, and customer profiles.
What is Database Management System? : What is Database Management System? Collection of interrelated data
Set of programs to access the data
DBMS contains information about a particular enterprise
DBMS provides an environment that is both convenient and efficient to use.
Database Applications:
Banking: all transactions
Airlines: reservations, schedules
Universities: registration, grades
Sales: customers, products, purchases
Manufacturing: production, inventory, orders, supply chain
Human resources: employee records, salaries, tax deductions
Databases touch all aspects of our lives
How is it Better ? : How is it Better ? In the early days, database applications were built on top of file systems.
Drawbacks of using file systems to store data:
Data redundancy and inconsistency
Multiple file formats, duplication of information in different files
Difficulty in accessing data
Need to write a new program to carry out each new task
Data isolation — multiple files and formats
Integrity problems
Integrity constraints (e.g. account balance > 0) become part of program code
Hard to add new constraints or change existing ones
(Cont.) : (Cont.) Atomicity of updates
Failures may leave database in an inconsistent state with partial updates carried out
E.g. transfer of funds from one account to another should either complete or not happen at all
Concurrent access by multiple users
Concurrent accessed needed for performance
Uncontrolled concurrent accesses can lead to inconsistencies
E.g. two people reading a balance and updating it at the same time
Security problems
A Table in Database : : A Table in Database : Fields and their values: