Transcript Lecture 6: An Introduction to Databases

What is Data?
What is the difference between Data and
Information?
Examples of a Database:
•Student Records at UCC
•Credit Card details
•Directory Enquiries
•Insurance Broker
•Library System
What is data?
 What is data?
 Data is the raw material from which information is
obtained
 The processing of data consists of manipulating it
into a form which provides information in a format
that is meaningful and usable to the manager or
other end-user
 Arrival of computer processing meant this process
was ‘mimicked’.
 Automation of existing systems. This is a traditional
file-based system
History of Information:
 Initially the information needs of an organisation
were met using a ‘manual system’. This system was
very labour intensive.
 With the arrival of computers, the manual filing
system was moved on to a computer. This early use
of computers for gathering information was called
the ‘file based approach’.
What is a file-based system?
 “A collection of application programs that
perform services for the end-users such as the
production of reports. Each program defines
and manages its own data.” (Connolly & Begg)
 An early attempt to computerise the manual
filing system used
 The operation of these systems closely
resembles that of a manual system. All that is
really achieved is the automation of the existing
system.
File Based Approach
APPLICATIONS
PAYROLL
PROGRAM
ADMIN.
PROGRAM
PROJECT
SCHEDULING
PROGRAM
DATA HELD
RESPONSIBILITY
HELD
Employee Name, Age,
Address, Hours, Pay
Rate
Payroll Dept.
Dept. Name, Employee
Name, Emp. Address,
Office Location
Dept. Managers
Project Name, Start
Date, Staff Name, Staff
Address, Project Hours
Project Leaders
What are the limitations of the file-based
system?
 Separation and isolation of data
 Decentralised data makes cross-referenced
searching slow and difficult
 Duplication of Data
 Wastes time and money for entering and
storage, leads to corruption of data integrity
 Program-Data Dependence
What are the limitations of the file-based
system?
 Incompatibility of files
 Structure and format is dependent on the
development language and platform of the
application
 Fixed queries and proliferation of application
programs
 Ad Hoc querying and reporting code to be
written from scratch
What is a Database?
 “a shared collection of logically related data (and a
description of this data), designed to meet the
information needs of an organisation” (Connolly &
Begg)
 Implications? Centralised (minimal duplication), selfdescribing (program independent to an extent),
logical structure (entities, attributes and
relationships).
Advantages of a Database:
 Data Integrity is easier to maintain as all data is
held in on central location
 A database system allows for ad-hoc queries
and caters to complex questions involving the
interaction and relationships between the
various data items in the database to be
investigated
 Security
 Minimisation of data duplication
 Control of data redundancy
 Improved Maintenance
Disadvantages of a Database:
 Complexity – increased functionality means the
system is more complex and sophisticated in
structure
 Size – complexity and functionality makes the
DBMS a large piece of software, taking up a lot of
space
 Cost of DBMSs – the cost can vary depending on
functionality required and the environment
 Additional Hardware Costs
 Cost of Conversion - conversion of existing systems
 High Impact of Failure - as a result of centralisation
What is a DBMS?
 The DBMS is a piece of software whose main
function is to organise data so it can be retrieved,
modified or updated at will. It is the link between
the user and the data, giving access to the data
required for the systems and their application
programs.
 “A software system that enables users to define,
create, and maintain the database and provides
controlled access to this database” (Connolly &
Begg).
Database Management System
APPLICATIONS
DATA HELD
PAYROLL
PROGRAM
Database
ADMIN.
PROGRAM
PROJECT
SCHEDULING
PROGRAM
DBMS
Employee
Administration
and project
Details
Explanation of a DBMS
 In the database structure, each system draws its data
via the database management system, so each
system’s program interacts with the DBMS rather
than the database files themselves (e.g MS Access)
 A DBMS can be described as an intelligent filing
cabinet, as it performs all the functions of an
efficient filing clerk
Components of a DBMS:
 Data definition language is used to define the
database (types, structure and constraints)
 Data Manipulation Language is used to insert,
update, delete and retrieve data. Utilises a flexible,
ad hoc, query language
 There are two types of query language, procedural
(one record at a time, “specifies how”) and nonprocedural (sets of records, “specifies what”).
 Access control includes security, integrity,
concurrency, recovery and catalogues.
Components of a DBMS:
 End-users use VIEWS which makes the DBMS
transparent in its activities
 A DBMS consists of hardware (machines, network
connections, physical storage), software (OS,
DBMS, applications), data, procedures and people
(administrators, designers (logical and physical),
programmers and end-users.
 Advantages: Less redundancy, improved
consistency, information, integrity, security,
scalability, flexibility, productivity, concurrency,
maintenance and recovery.
 Disadvantages: complexity, size, cost,
generalisation, high impact of failure.
Roles in Database Management
System
•
•
•
•
Database Administrator
Database Designers
Application Programmers
End-Users
Architecture
 Most DBMS’s use a three-level architecture: External,
Internal and Conceptual
 Internal - describes how the data is stored in the
database (space allocation, compression, encryption
etc.) and interfaces with the OS to manage files in
physical storage
 Conceptual - Describes what data is stored and the
relationships between data
 External - Defines the users view of the data
Reasons for Three-Tier Architecture