Database & Database Users

Lecturer:
M.Zalmai “Rahmani”
rahmani.zalmai@gmail.com
Advanced Database Systems
Database & Database Users
Lecture 01
Azma Institute
Database Department

Database Applications
Banking:
For customer information, accounts, loans and banking transactions.
Universities:
For student information, course registrations, and grades.
Sales:
For customer, product, and purchase information.
Airlines:
For reservations and schedule information.

Credit card transactions:
For purchases on credit cards and generation of monthly statements
“printed record of account activity”.
Human resources:
For information about employees, salaries, payroll taxes and benefits, and
for generation of pay checks “salary”.
Telecommunication:
For keeping records of calls made, generating monthly bills, maintaining
balances on prepaid calling cards, and storing information about the
communication network.

Finance:
For storing information about sales, and purchases of financial instruments
such as stocks and bonds.
Manufacturing:
For management of supply chain and for tracking production of items in
factories, inventories of items in warehouses/stores, and orders for items.

Databases play a critical role in almost all areas in which
computers are used!
Brainstorming Summary

What is database?
A database is a collection of related data.
By data, we mean known facts that can be recorded and that have implicit
meaning.

Database Properties
Represents some aspect of the real world that is called the miniworld.
Changes to the miniworld are reflected in the database.
Is a logically coherent collection of data with some inherent meaning.
A random assortment of data cannot correctly be referred to as a database.
Is designed, built, and populated with data for a specific purpose.

Size & Complexity of a Database
A database can be of any size and complexity
• Example for a small database:
Personal DB with addresses with only a few hundred records (each with a
simple structure)
• Example for a large database:
Amazon.com: with more than 20 million of books, CDs, eBooks,
magazines, journals and etc. In a DB with the size of 2 terabytes

Database Management Systems
(DBMS)
A Database Management System (DBMS) is a collection of interrelated data
and set of programs to access those data.
• The collection of data, usually referred to as the database, contains
information related to an enterprise.
Is a collection of programs that enables users to create and maintain a
database.

Database Management Systems
(DBMS)
DBMS fulfils(Do) different purposes:
• Defining : Specifying the data types, structures, and constraints for the data
to be stored in the database.
• Constructing : Process of storing the data itself on some storage medium
that is controlled by the DBMS.
• Manipulating : Adding, Updating, Deleting ….
• Sharing databases among various users and applications

(DBMS)
MS Access
MySQL (Open Source)
SQL-Server (Microsoft)
Oracle
PostgreSQL
FoxPro
SQLite

Application Program /
Database System
An application program accesses the database by sending queries or
requests to the DBMS.
• A query (question, inquiry) is the interaction with the database, e.g.
retrieving or manipulating data.
Database System
• The database, the DBMS software, and the application program together
are called a database system.

Example of a Database System
UNIVERSITY database
• Defining the database: we must specify the structure of the records of each
file by specifying the different types of data elements to be stored in each
record .
• Constructing the database: we store data to represent each student,
course, section, grade report, and prerequisite as a record in the appropriate
file
• Manipulating the database: Querying and updating

Characteristics of the Database
A number of characteristics distinguish the database approach from the
traditional approach of programming with files :
• Self Describing nature of the database
Database system contains not only the database itself but also a complete
definition or description of the database structure and constraints.

Data Abstraction
• Allows program-data independence and program-operation independence
MultipleViews of the Data
• Some users may not need to be aware of whether the data they refer to is
stored or derived
• One user of the database may be interested only in the transcript of each
student;
• A second user, who is interested only in checking that students have taken all
the prerequisites of each course they register for

Sharing of Data and MultiuserTransaction Processing
• ConcurrencyControl to manage transactions
A transaction is an executing program or process that includes one or more
database accesses, such as reading or updating of database records

Actors on the scenes
What roles do people take around a database system?
• Database Administrators
• Database Designers
• End Users
• Application Programmers (Software Engineers)

Database Administrators
• When the database is designed and implemented it is handed over to the DB
administrator
• person responsible for the DB during its lifetime
• management of user accounts, hardware resources, backups, etc.

Database Designers
• The database designers conceptually design and implement the DB
• Analyze requirements for the DB
• Gathering of information about the application field
• Conceptual schema. (conceptual = of an idea or concept)
• Choice of DBMS

End Users
• The people who will use the DB when it is finished
• Normally little technical knowledge
• Use the DB
Application Programmers
• Programmers that write programs that use the DB
• Programmers of a graphical user interface (GUI) for the database

Workers behind the scenes
People who are working behind the database scenes are as:
• DBMS system designers and implementers
• Design and implement the DBMS modules and interfaces as a software
package.
Tool developers
• Design and implement tools—the software packages that facilitate database
modelling and design, database system design, and improved performance.
Operators and maintenance personnel
• Responsible for the actual running and maintenance of the hardware and
software environment for the database system.

Advantages of using the DBMS
Controlling redundancy
Providing Storage Structures and SearchTechniques for Efficient Query
Processing
Providing Backup and Recovery
Providing Multiple User Interfaces
Representing Complex Relationships among Data
Enforcing Integrity Constraints
Permitting Inference and Actions Using Rules

Why don’t store on plain files?
Consider part of a savings-bank enterprise that stores information about all
customers and saving accounts.
• We need separate application programs that manipulate the files.
• A program to debit or credit an account
• A program to add a new account
• A program to find the balance of an account
• A program to generate monthly statements

Advantages of using file
systems
We would rather use plain files and develop additional software tools, if:
• The database is simple
• The actions on the data are simple
• No multi-user environment
Example: private address book, data can be even “stored” on paper

Disadvantages of using file
systems
Data redundancy and inconsistency:
• Since in File Systems we store all information in different files, so the same
information maybe duplicated in several files.
• Redundancy leads to higher storage and access cost.
• Redundancy also leads to data inconsistency

systems
Difficulty in accessing data
• What happen if someone asks about list of all customers who live in a special
city “kabul”, Since the original system did not predict this kind of list with
mentioned criteria
• File Systems do not allow needed data to be retrieved in a convenient and
efficient manner.
Data Isolation:
• Because data are scattered in various files, and files maybe in different
formats, writing new application programs to retrieve the needed data is not
that much easy.

systems
Problems
• Consider a program to transfer 100$ from accountA to account B.
Constrains:
If a system failure or crush occurs during the execution of the transfer.
Possibility:
100$ remove from accountA, but not added to account B.
• It is essential to database consistency that either both the debit and credit
occur, or that neither occur.

systems
Concurrent access exception
• Uncontrolled multi-user access can have undesirable results!
• Consider bank accountA, has 500$. If two customers at the same time
withdraw (one 50$ and the other 100$) from accountA, the result of the
concurrent executions may leave the account in an incorrect state.
Security Problems
• Data should not be accessible for all users.
• No Mechanism for giving certain privileges to certain users.
• No mechanisms for user authorization and encryption in file-processing
system.

Advantages of database
systems
Fast, complex queries on data are possible:
• Example:
We would like to know the names of all employees who live in Kabul and
have a salary higher than the average salary.
• It is not easy/can take a lot of time to extract this information from a file.
• It is even more difficult/impossible to “link” data that is stored across several
isolated files.

systems
Redundancy control and consistency control
• Example:
Both, university administration and individual departments store data
about students in isolated files
• Same data is stored several times (=redundancy)
• More storage space necessary
• Difficult to maintain consistency (for example if
Administration updates address of student, but it is not updated in the files
of department)

systems
Support of multi-user environment
• Uncontrolled multi-user access can have undesirable results!
Example:
if userA and user B read a file at the same time, userA writes data into the
file and stores it, user B writes data and stores it data of userA is
overwritten!
Database Systems provide mechanisms to control multiuser access
(concept of “Transactions”)

systems
Prevention of data loss
• Power failure, hardware/software failure can result in loss of data
• Database Systems provide more sophisticated recovery components to
backup and restore data than File Systems

systems
Security Issues
• Often we would like to control which users get access to what parts of the
data (read or even manipulate data)
• Database systems provide mechanisms for user authorization and
encryption

Disadvantages of database
systems
Complex, expensive software and hardware
Skilled professionals and user training necessary
Therefore high start-up costs

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