3 / 12
Databases
MIS105
Lec14
11
Irfan Ahmed Ilyas
Lecture Objectives
• Integrated File Approach for saving data
– Benefits/ Drawback
• Database Accessing Approach
– File based Programs
– DBMS based access
• Introducing DBMS
– Working of a basic DBMS
– Main DBMS Features
11 • Users in a DBMS Environment
02/3/2002
Prepared By: Irfan Ilyas
2
…Database Implementation Approaches
• Integrated File Approach
11
– Data is scattered among many different data files
– Each file is saving data relevant to its subject only
– Files are linked together through data pointers
(common field values)
– The integrated collection of these data files is normally
contained in one single disk file (database file)
– Disadvantage: Cross-referencing across the files is
needed for detailed reporting
– Benefit: Data duplication is minimized which removes
the updation anomalies
02/3/2002
Prepared By: Irfan Ilyas
3
Integrated File Database Example
• A Student Grade Database
• STUDENT – saving only student personal information
• GRADE_REPORT – saving only grade information about
student courses
– The process which decompose data optimally among data
files is called Normalization.
STUDENT
Name
Smith
Brown
GRADE_REPORT
StudentID
17
17
8
8
8
8
11
02/3/2002
StudentNumber Class
17
8
Major
1 CS
2 CS
CourseCode
MATH2410
CS1310
MATH2410
CS1310
CS3320
CS3380
1
1
2
1
1
1
Prepared By: Irfan Ilyas
SectionCode
Grade
B
C
A
A
B
A
4
…Integrated File Database Example
• For detailed information, a cross-referencing activity is needed
– While reading GRADE_REPORT, other student details can be found by using
the data pointer (StudentNumber) in the STUDENT file
• Data updation anomalies are removed
– Addition Anomaly: While adding a new student’s grade in GRADE_REPORT
file, no need to check for any data consistency .
– Deletion Anomaly: Deleting all grades for any student, doesn’t delete the
student information from STUDENT file.
– Modification Anomaly: A student’s attribute change in STUDENT file (like
Name) doesn’t need to be reflected in his grade records in GRADE_REPORT
file (key attribute is an exception).
11
02/3/2002
STUDENT
Name
Smith
Brown
GRADE_REPORT
StudentID
17
17
8
8
8
8
Prepared By: Irfan Ilyas
StudentNumber Class
17
8
Major
1 CS
2 CS
CourseCode
MATH2410
CS1310
MATH2410
CS1310
CS3320
CS3380
1
1
2
1
1
1
SectionCode
Grade
B
C
A
A
B
A
5
Accessing a Database
1. Directly Accessing the database files
•
Programs which directly work upon database files in order to
– handle data maintenance, like creating, defining, updating data, in files
– carry out the end-user job.
•
Any high level language like C++, Java etc. can be used to write such
programs
•
Disadvantages
– Structural Dependence
• These programs are very sensitive to the data file record structures
• A small change in the structure of any file’s record needs to change all
the programs working over it.
11
– End users are always dependant on programmers for even a simple
access to the database.
02/3/2002
Prepared By: Irfan Ilyas
6
1. File Based Application
Programs
Accounting
End User
Registration
End User
Accounting
Application
Registration
Application
Disk Storage
STUDENT
Name
Smith
Brown
Smith
Brown
Smith
Brown
StudentNumber Class
17
8
8
2
2
2
1
2
3
4
5
6
Major
CS
CS
CS
CS
CS
CS
Other End
Users…
Any other
application….
Disk Storage
Disk Storage
STUDENT
STUDENT
Name
Smith
Brown
Smith
Brown
Smith
Brown
StudentNumber Class
17
8
8
2
2
2
1
2
3
4
5
6
Major
CS
CS
CS
CS
CS
CS
Name
Smith
Brown
Smith
Brown
Smith
Brown
StudentNumber Class
17
8
8
2
2
2
1
2
3
4
5
6
Major
CS
CS
CS
CS
CS
CS
11
02/3/2002
Prepared By: Irfan Ilyas
7
…Accessing a Database
2. Using DBMS Software
•
DBMS Software is a collection of general purpose programs that
•
•
enables users to create and maintain an integrated file database
Separates the job of data maintenance from end-user use of stored data
Available as a packaged software, called General Purpose Database
Management System (DBMS)
• DBMS Main Features
– Data Structural Independence
• Different end-user applications can access database on disk through DBMS
• DBMS makes the applications unaffected with any structural change happened
in database
• DBMS uses control information data (Data Dictionary) to inform the
application programs about the structural details of the database files
• Data Dictionary is updated automatically by DBMS in case of any structural
change done on the database
11
02/3/2002
Prepared By: Irfan Ilyas
Chapter 11 (p268)
8
Example: Data Dictionary
DBMS User
End User
End User
Application S/W
DBMS Software
A Database File on disk
STUDENT
Name
Smith
Brown
GRADE_REPORT
StudentID
17
17
8
8
8
8
StudentNumber
Class
17
8
Major
1 CS
2 CS
CourseCode
MATH2410
CS1310
MATH2410
CS1310
CS3320
CS3380
1
1
2
1
1
1
A Database Example
SectionCode
Grade
B
C
A
A
B
A
Dictionary Data
11
Address
B14
B15
B16
B17
B18
B19
Table
STUDENT
STUDENT
STUDENT
STUDENT
………
Fields
Name
StudentID
Class
Major
……….
Types
Character
Character
Number
Character
………
Size
30
8
2
5
………
Database’s Data Dictionary
02/3/2002
Prepared By: Irfan Ilyas
9
.. 2. Using DBMS Software
• .. DBMS Main Features
– Data Query Language
• DBMS lets its users/ application programs to access database
by making use of some query language
• A query language is a set of standardized commands to
perform different database maintenance activities
• SQL (Structured Query Language) is the most widely used.
• Examples of SQL commands are
–
–
–
–
11
02/3/2002
CREATE TABLE – to create new data tables (files)
SELECT – to display selected data records
UPDATE – to modify selected data records
Chapter 11 (p295)
… and many others.
Prepared By: Irfan Ilyas
10
Details of DBMS Components
• Database Engine
– Controls all the data management activities (like
database creation, retrieval, validation, manipulation
etc.)
• DBMS Interface Objects
11
– Easy to use graphical interfaces (menus, buttons,
wizards etc.) to access the underlying database
– Each of these objects are interacting with database
engine in the background through SQL commands
02/3/2002
Prepared By: Irfan Ilyas
11
A Look to Database Management
Systems
• Create, modify, gain access to databases
• Subsystems
Chapter 11,
– DBMS engine
pg294
– Data definition subsystem
• Data dictionary
– Data manipulation subsystem
• SQL
11
– Application generation subsystem
– Data administration subsystem
• Database administrators
02/3/2002
Prepared By: Irfan Ilyas
12
A Working DBMS
DBMS Package
End User
Database
Application
Interface
Objects
Database User/
Operator
S Q LC OM MAN D S
Programming Interface
Programmers
Database Engine
Data Definition
Subsystem
Database Creation
Subsystem
Database Security
Subsystem
Disk Storage
Integrated File
Database
11
02/3/2002
Prepared By: Irfan Ilyas
STUDENT
Name
Smith
Brown
GRADE_REPORT
StudentID
StudentNumber Class
17
8
17
17
8
8
8
8
CourseCode
MATH2410
CS1310
MATH2410
CS1310
CS3320
CS3380
Major
1 CS
2 CS
SectionCode Grade
1B
1C
2A
1A
1B
1A
13
Database Personnel
Chapter 11 (p276)
• End Users
– Requires access to the database for their jobs
– Perform querying, updating and reporting on the stored database
– Usually provided with a user friendly application program interface
• Database Designers
– Identifying the logical/ structural database picture for an environment
• Database Administrators
– Controlling security, structural updates and performance issues for a
corporate database
11
• System Analysts and Application Programmers
– Responsible for generating easy to use application programs for the end
user requirements
02/3/2002
Prepared By: Irfan Ilyas
14
Users in a DBMS Environment
End User
Database
Designer
Database
Administrator
Information System
Application Program(s)
Data Definition
Module
Database Creation
Module
Data Manipulation
Module
DBMS
Modules
Database
11
02/3/2002
Prepared By: Irfan Ilyas
15
11
02/3/2002
Prepared By: Irfan Ilyas
16