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LECTURE1: PRINCIPLES OF DATABASES
Ref. Chapter1
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Chapter1 - Objectives
• Problems with file-based approach.
• Database concepts.
• Database Management System (DBMS).
• Major components of the DBMS environment.
• Users involved in the DBMS environment.
• Advantages and disadvantages of DBMS.
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Introduction
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Examples of Database Applications
File-Based Systems
• Collection of application programs that perform
services for the end users (e.g. reports).
• Each program defines and manages its own data.
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File-Based Systems
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Limitations of File-Based Approach
1. Separation and isolation of data
• Each program maintains its own set of data.
• Users of one program may be unaware of potentially useful data held by other programs.
2. Duplication of data
• Same data is held by different programs.
• Wasted space and potentially different values and/or different formats for the same item.
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Limitations of File-Based Approach
3. Data dependence
• File structure is defined in the program code.
• Definition of data was embedded in application programs, rather than being stored separately and independently.
4. Incompatible file formats
• Programs are written in different languages, and so cannot easily access each other’s files.
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Solution …
DATABASE APPROACH
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Database Approach
Main terms:
Data
Information
Database
Metadata /System Catalog / data Dictionary
Entity
Attribute
Relationship
Database Management System
Database Application Program
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Database Approach
Data: Known facts that can be recorded and have an implicit
meaning. Ex: What does 3421 means?
Notice there are different types of data
numbers, strings, date, time
Text, picture, audio, video, graphics …
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Database Approach
Data versus Information
Data itself has no meaning without meta data which describes data
For example : 1012674, 28761, 153
Does not give us any information, but knowing the meta data that explains data : Staff_ID, Phone Number, room number
Information : is the data you process in a manner that makes it meaningful.
Data is what you store in database
Information is what you retrieve from database
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Staff_ID Phone Number room number
1012674 28761 153
Database Approach
Database: Shared collection of logically related data and a description of this data, designed to meet the information needs of an organization.
Metadata (system catalog/data dictionary): The description of the data, used to enable program–data independence.
Data: name city birth Metadata: name - string, length<10
Khaled Dammam 01/01/70 city – string, length<15
Sara Abha 01/03/01 birth – date, format DD/MM/YY
Examples all data required for the management of student records in a university.
all data required for the management of books and borrowers in a library.
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Database Approach
Logically related data comprises entities, attributes, and relationships of an organization’s information.
Entity: a distinct object( a person, place, thing, event) in the organization that is to be represented in the database.
Attribute: is a property that describes some aspect of the object that we wish to record.
Relationship: is an association between entities.
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Example of a Database
Mini-world: Some part of the real world about which data is stored in a database.
Mini-world for the example: Part of a UNIVERSITY environment.
Some mini-world entities:
STUDENTs
COURSEs
SECTIONs (of COURSEs)
Grade Report
Prerequiests
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Example of Database Requests
Based on the previous database:
Retrieve the transcript – a list of all courses and grades – of ‘Smith’
List the names of students who took the section of the ‘Database’ course offered In fall 2008 and their grades in that section
List the prerequisites of the ‘Database’
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Example of a Database
Some mini-world relationships:
SECTIONs are of specific COURSEs
STUDENTs take SECTIONs
COURSEs have prerequisite COURSEs
INSTRUCTORs teach SECTIONs
COURSEs are offered by DEPARTMENTs
STUDENTs major in DEPARTMENTs
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Database Management Systems
Database Management System (DBMS)
A software system that enables users to
create, maintain, and query the database
Most DBMSs now have facilities that make data access fast, reliable, secure and easy
Example DBMSs
Oracle
MS Access
MySQL
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Application programs
Database Application : is a collection of data and
the programs that interacts with the database by
issuing an appropriate request (typically an SQL
statement) to the DBMS.
built on top of DBMS
to satisfy end users special requirements and
preferences
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Examples of Database Applications
Purchases from the supermarket
PNU Student Registration
PNU Library
Saudi Airline Reservation
Purchases using your credit card
Booking a holiday at the travel agents
Using the Internet
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Database System
Database System: The DBMS software together with the
data itself. Sometimes, the applications are also included.
(DB + DBMSs + Application program)
To manage large amounts of data
Efficiently
Reliably
Securely
conveniently
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Database Approach
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Main Characteristics of the Database Approach
1. Self-describing nature of a database system: A DBMS
catalog stores the description of the database. The
description is called (meta-data). This allows the DBMS
software to work with different databases.
2. Insulation between programs and data: Called program-data
independence. Allows changing data storage structures and
operations without having to change the DBMS access
programs (application program).
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Main Characteristics of the Database Approach
3. Data Abstraction: A data model is used to hide storage
details and present the users with a conceptual view of the
database.
4. Support of multiple views of the data: Each user may see a
different view of the database, which describes only the
data of interest to that user.
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Views
Allows each user to have his or her own view of the
database.
A view is essentially some subset of the database.
Benefits:
Reduce complexity
Provide a level of security
Present a consistent, unchanging picture of the structure
of the database, even if the underlying database is
changed
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Main Characteristics of the Database Approach
5. Sharing of data and multiuser transaction processing :
allowing a set of concurrent users to retrieve and to update
the database.
Transaction: executing program or process that includes one or more
database accesses, such as reading or updating of DB record.
Concurrency control within the DBMS guarantees that each transaction
is correctly executed or completely aborted.
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Components of DBMS Environment
1. Hardware
Can range from a PC to a network of computers.
2. Software
DBMS, operating system, network software (if necessary)
and also the application programs.
3. Data
4. Procedures
Instructions and rules that should be applied to the design
and use of the database and DBMS.
5. People
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Components of DBMS Environment
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DBMS App
Program
DB
User
Requirement Procedure
DBA
Naïve End User
Application programmer
DB Designer System Analyst
H/W
Design
Communicate
Manage
Write Write
Program
Use
Use
Roles in the Database Environment
Sophisticated End User
Roles in the Database Environment
System Analyst: Determine the user requirements and develop the system specifications.
Database Designers:
responsible for defining the content, the structure, the constraints, and functions or transactions against the database.
Application Programmer
Implement programs meet the end user needs.
Test , debug , document, and maintain transactions.
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Roles in the Database Environment
Database administrators: responsible for:
authorizing access to the database.
coordinating and monitoring the DB use.
acquiring software, and hardware resources.
monitoring efficiency of operations.
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Roles in the Database Environment
End-users: they use the data for queries, reports and some of them actually update the database content.
Categories of End-users:
Naïve : (Queries / modifies data)
- they make up a large section of the end-user population.
- They use previously well-defined functions in the form of “canned transactions” against the database.
- Examples: bank-tellers or reservation clerks.
Sophisticated : Forms requests in a database query language.
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Advantages of Using the Database Approach
Controlling redundancy in data storage and in
development and maintenance efforts.
Sharing of data among multiple users.
Restricting unauthorized access to data.
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Advantages of Using the Database Approach
Providing backup and recovery services.
Providing multiple interfaces to different classes
of users.
Enforcing integrity constraints on the database.
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Disadvantages of Database Approach
Complexity
Cost of DBMS
Additional hardware costs
Performance
Higher impact of a failure
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References
Main Reference:
“Database Systems: A Practical Approach to
Design, Implementation and Management.”
Thomas Connolly, Carolyn Begg.
5th Edition, Addison-Wesley, 2009.
Supplementary:
Fundamentals of Database Systems", Ramez
Elmasri, Shamkant B. Navathe, Addison
Wesley, The Latest Edition.
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