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.

APPLICATIONS

PAYROLL

PROGRAM

ADMIN.

PROGRAM

PROJECT SCHEDULING

PROGRAM

DATA HELD

Employee Name, Age, Address, Hours, Pay Rate

Dept. Name, Employee Name, Emp. Address, Office Location

Project Name, Start Date, Staff Name, Staff Address, Project Hours

Payroll Dept.

Dept. Managers

Project Leaders

RESPONSIBILITY HELD

What are the limitations of the file-based system?Separation and isolation of dataDecentralised data makes cross-

referenced searching slow and difficultDuplication of DataWastes 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 filesStructure 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), self-describing (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 locationA 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

SecurityMinimisation of data duplicationControl of data redundancyImproved 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

systemsHigh 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).

DBMS

PAYROLL

PROGRAM

ADMIN.

PROGRAM

PROJECT SCHEDULING

PROGRAM

APPLICATIONS DATA HELD

DatabaseEmployee

Administration and project Details

Explanation of a DBMSIn 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 non-procedural (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 activitiesA 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

ArchitectureMost DBMS’s use a three-level architecture:

External, Internal and ConceptualInternal - 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