INTRODUCTION-DBMS

Introduction

· A database management system (DBMS) is a collection of data and an integrated set of programs that access that data.

Example: PSH keeps information about each student name, social security number, standing, address etc., this data makes up the database

· Programs (or parts of programs) are used to add new students, to change a student's address or standing, to retrieve information about a student.

Goals of a DBMS:

· Manage large bodies of information

· Provide convenient and efficient ways to store and access information

· Secure information against system failure or tampering

· Permit data to be shared among multiple users

Why DBMS’s are needed?

Alternative: store information in files, and write programs as needed to modify these files and retrieve information.

A file processing system is a collection of files and programs that access/modify these files

Problems with file processing systems:

· Data redundancy and inconsistency

· Difficulty of accessing data

· Problems with concurrent access

Example: Assume I'm paying for groceries with my MAC card at the same time my pay check is being deposited (and my bank uses a file processing system)

withdrawal program	deposit program
1. read balance from checking account file as $55
	2. read balance from checking account file as $55
3. subtract $50 (for groceries)
4. update checking account file (new balance: $5)
	5. add $100 (my salary)
	6. update checking account file (new balance: $155)

It is difficult to prevent such problems unless programs (example: withdrawal and deposit) are coordinated or integrated.

Security problems

· Not all users should have access to all data

· Example: Bank payroll personnel shouldn't know my checking account balance

· Difficult to enforce security in an ad hoc system

Integrity problems

· Data may need to satisfy certain conditions, called consistency constraints.

· Example: Account balances should never fall below $0

· Difficult to enforce/add/change consistency constraints in a file processing system

DBMS's were developed to remedy these problems