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Chapter 1
Introduction to Databases
Transparencies
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Chapter 1 - Objectives
x Typical functions of a DBMS.
x Major components of the DBMS environment.
x Personnel involved in the DBMS environment.
x History of the development of DBMSs.
x Advantages and disadvantages of DBMSs.
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Examples of Database Applications
x Purchases from the supermarket
x Purchases using your credit card
x Booking a holiday at the travel agents
x Using the local library
x Taking out insurance
x Renting a video
x Using the Internet
x Studying at university
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File-Based Systems
x Collection of application programs that
perform services for the end users (e.g. reports).
x Each program defines and manages its own
data.
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File-Based Processing
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Limitations of File-Based Approach
x 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.
x Duplication of data
Same data is held by different programs.
Wasted space and potentially different valuesand/or different formats for the same item.
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Limitations of File-Based Approach
x Data dependence
File structure is defined in the program code.
x Incompatible file formats Programs are written in different languages, and so cannot
easily access each others files.
x
Fixed Queries/Proliferation of application programs Programs are written to satisfy particular functions.
Any new requirement needs a new program.
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Database Approach
x Arose because: Definition of data was embedded in application
programs, rather than being stored separately andindependently.
No control over access and manipulation of databeyond that imposed by application programs.
x Result: the database and Database Management System
(DBMS).
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Database
x Shared collection of logically related data (anda description of this data), designed to meet theinformation needs of an organization.
x System catalog (metadata) provides descriptionof data to enable programdata independence.
x Logically related data comprises entities,attributes, and relationships of anorganizations information.
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Database Management System (DBMS)
x A software system that enables users to define,
create, maintain, and control access to the
database.
x (Database) application program: a computer
program that interacts with database by
issuing an appropriate request (SQLstatement) to the DBMS.
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Database Management System (DBMS)
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Database Approach
x Data definition language (DDL).
Permits specification of data types, structures and
any data constraints.
All specifications are stored in the database.
x Data manipulation language (DML).
General enquiry facility (query language) of thedata.
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Database Approach
x Controlled access to database may
include:
a security system
an integrity system
a concurrency control system
a recovery control system
a user-accessible catalog.
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Views
x Allows each user to have his or her own view of
the database.
x A view is essentially some subset of the
database.
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Views - Benefits
x Reduce complexity
x Provide a level of security
x Provide a mechanism to customize the
appearance of the database
x Present a consistent, unchanging picture of the
structure of the database, even if the
underlying database is changed
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Components of DBMS Environment
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Components of DBMS Environment
x Hardware
Can range from a PC to a network of computers.
x Software
DBMS, operating system, network software (ifnecessary) and also the application programs.
x Data
Used by the organization and a description of
this data called the schema.
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Components of DBMS Environment
x Procedures
Instructions and rules that should be applied to
the design and use of the database and DBMS.
x People
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Roles in the Database Environment
x Data Administrator (DA)
x Database Administrator (DBA)
x
Database Designers (Logical and Physical)x Application Programmers
x End Users (naive and sophisticated)
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History of Database Systems
x First-generation Hierarchical and Network
x Second generation Relational
x Third generation Object-Relational
Object-Oriented
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Advantages of DBMSs
x Control of data redundancy
x Data consistency
x More information from the same amount of
datax Sharing of data
x Improved data integrity
x Improved security
x Enforcement of standards
x Economy of scale
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Advantages of DBMSs
x Balance conflicting requirements
x Improved data accessibility and responsiveness
x Increased productivity
x Improved maintenance through data
independence
x Increased concurrency
x Improved backup and recovery services
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Disadvantages of DBMSs
x Complexity
x Size
x Cost of DBMS
x Additional hardware costs
x Cost of conversion
x Performance
x Higher impact of a failure
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