Lecture - Objectives
◆ Some common uses of database systems.
◆ Characteristics of file-based systems.
◆ Problems with file-based approach.
◆ Meaning of the term database.
◆ Meaning of the term Database Management
System (DBMS).
Lecture - Objectives
◆ Typical functions of a
◆ Major components of
◆ Personnel involved in
DBMS.
the DBMS environment. the DBMS environment.
◆ History of the development of DBMSs.
◆ Advantages and disadvantages of DBMSs.
Examples of Database Applications
◆ Purchases
◆ Purchases
◆ Booking a
from the supermarket
using your credit card
holiday at the
travel
agents
◆ Using the local library
◆ Taking out insurance
◆ Renting a video
◆ Using the Internet
◆ Studying at university
File Systems & Database Systems
Data Versus Information
◆ Data is a collection of facts.
◆ Information is process data.
◆ Good, timely, relevant information
in taking a decision.
is
essential
◆ A
good decision is vital for organization.
File-Based Systems
Terminologies
◆ Data : Raw Facts
◆ Field : Group of characters
meaning
with specific
◆ Record : Logically connected fields that
describe a person, place, or a thing
◆ File: Collection of related records
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.
File-Based Processing
Limitations of File-Based Approach
◆ 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.
◆ Duplication of data
–
–
Same data is held by different programs.
Wasted space and potentially different values and/or different formats for the same item.
Lack of data integrity
Data anomalies
–
–
Limitations of File-Based
Approach
◆ Data dependence
– File structure is defined in
the program code.
◆ Incompatible file formats
– Programs are written in different languages, and
cannot easily access each other’s files.
so
◆ Fixed Queries/Proliferation of application
programs
– Programs are written to satisfy particular functions.
– Any new requirement needs a new program.
Limitations of File-Based Approach
◆ Structural Dependence
– Change in file structure requires modification
related programs
of
Database Approach
◆ Arose because:
– Definition of data was embedded in application
programs, rather than being stored separately and
independently.
– No control over access and manipulation of data beyond that imposed by application programs.
◆ Result:
– the database and Database Management System
(DBMS).
Database
◆ Shared collection of logically related data (and a
description of this data), designed to meet the information needs of an organization.
◆ System catalog (metadata) provides description
of
data to enable program–data independence.
-Metadata (data about data or data about the containers of data)
◆ Logically related data comprises entities,
attributes, and relationships of an organization’s
information.
Database Management System (DBMS)
◆ It is a software system that enables users to
define, create, maintain, and control access to
database.
the
◆ The DBMS is the software that interacts with
the
users’ application programs and the database.
Database Management System (DBMS)
Database Management
System
(DBMS)
◆ User
–
–
–
Create
Maintain
Generate
◆ The database
approach is illustrated in the figure
based on the file approach. It shows the Sales and
Contracts Departments using their application
programs to access the database through the DBMS.
Database Management System (DBMS)
Database Approach
DBMS provides the following facilities:
◆ Data definition language (DDL).
– Permits specification of data types, structures any data constraints.
– All specifications are stored in the database.
◆ Data manipulation language (DML).
and
– General enquiry facility (query language) of the
data.
– Allows users to insert, update, delete, and retrieve data from the database
Database Approach
◆ Controlled access
May include:
to database.
–
–
–
–
–
a security system
an integrity system
a
a
a
concurrency control system
recovery control system
user-accessible catalog.
Database Application Program
◆ (Database) application program: a computer
program that interacts with database by issuing an
appropriate request (SQL statement) to the DBMS.
◆ Users interact with the database through a number
of application programs that are used to create and
maintain the database and to generate information.
Views
◆ Allows each user to have his or her own view of
the database.
◆ A view is essentially some subset of the
database.
Views - Benefits
◆ Reduce complexity
◆ Provide a level of security
◆ Provide a mechanism to customize appearance of the database
the
◆ Present a consistent, unchanging picture of the
structure of the database, even if the underlying database is changed
Components of DBMS Environment
▪ Five major components in the DBMS environment
Components of DBMS Environment
◆ Hardware
– Can range from a PC to a network of
computers.
◆ Software
– DBMS, operating system, network software
(if
necessary) and also the application programs.
◆ Data
– Used by the organization and a description
of this data called the schema. It contains
both the operational data and the metadata
Components of DBMS Environment
◆ Procedures
– Instructions and rules that should be applied to
the design and use of the database and DBMS.
◆ People
Database Design
Database design is the process of producing a
detailed data model of a database. (Structure)
◆ Importance of Good Design
– Poor design results in unwanted data redundancy
– Poor design generates errors leading to bad decisions
Roles in the Database Environment
◆ Data Administrator (DA)
◆ Database Administrator (DBA)
◆ Database Designers (Logical and Physical)
◆ Application Programmers
◆ End Users (naive and sophisticated)
Database Design
Database designers
◆ Logical database designer
– The logical database designer is concerned with identifying the data (that is, the entities and attributes), the relationships between the data, and the constraints on the data that is to be stored in the database.
Database Design
Database designers
◆ Physical database
designers
designer decides how the logical
–
physical database
database design is to be physically realized. This
involves:
mapping the logical database design
selecting specific storage structures and access
–
–
History of Database Systems
◆ First-generation
– Hierarchical and Network
◆ Second generation
– Relational
◆ Third generation
– Object-Relational
– Object-Oriented
Advantages of DBMSs
◆ Control of data redundancy
◆ Data consistency
◆ More information from the
data
◆ Sharing of data
◆ Improved data integrity
◆ Improved security
◆ Enforcement of standards
◆ Economy of scale
same
amount
of
Advantages of DBMSs
◆ Balance conflicting requirements
◆ Improved
◆ Increased
◆ Improved
data accessibility and
productivity maintenance through
responsiveness
data
independence
◆ Increased concurrency
◆ Improved backup and recovery services
Disadvantages of
DBMSs
◆ Complexity
◆ Size
◆ Cost of DBMS
◆ Additional hardware
◆ Cost of conversion
◆ Performance
costs
◆ Higher impact of a failure