CSE1204 - Information Systems 1

Revision

Subject Overview System concepts and information systems Systems development and the SDLC Information gathering Modelling Process modelling using DFDs Low-level processes: minispecs

Subject Overview System design principles Communicating using documentation and

presentations Working in teams Ethics and professional practice Roles in the SDLC Project management Quality - product and process Types of information systems

System concepts and information systemsA system: An inter-related set of components that

interact to accomplish goals system elements

• components, inter-related components, a boundary, a purpose, an environment, interfaces, input, processing, output, feedback, constraints

Information systems An Information System is a formal

arrangement of people, data, processes integrated to help manage complexity and to support and improve business operations, as well as supporting the problem-solving and decision-making activities of managers.

It transforms Data into Information

Any information system performs four main functions:

data input - recording information data storage/retrieval - keeping information data processing - transforming information data output - displaying/presenting information

Functions of an Information System

Benefits of an Information SystemA good information system ensures:-

the right information to the right degree of accuracy when it is required in the right format/layout to the right people in the most efficient way possible

Systems development and the SDLC The need to build new information systems or

change existing ones comes about because:• there are problems in the way in which

existing systems operate; or• changes in circumstances create

opportunities to improve things by doing them differently; or

• there are external requirements or pressures, e.g. new government legislation

The Systems Development Life CycleThe SDLC provides: a systematic and orderly approach to solving business

problems a means of managing, directing, monitoring and

controlling the process of system building, including:

• a description of the process - steps to be followed

• deliverables - reports/programs/documentation/etc

• milestones - dates of completion of steps or deliverables

10

Systems Development Phases

Analysis

Design

Implementation

Review

Maintenance

Quality

Documentation

Ethics

Project Management

Analysts RoleInitiation

Systems DevelopmentActivities involved in building computer-

based information systems are:- identifying problems analysing and describing information and

processing needs designing solutions to meet those needs acquiring/building new systems implementing new systems maintaining information systems

Data GatheringThe data gathered should include: system description - how things work or should

work system problems - what is wrong or needs

improvement opportunities - identifying scope for innovation

or new ways of doing things what is technically possible what constraints exist

Data gathering techniques

Interviews

Questionnaires

Observation

Reports

System Documentation

Modelling Why do we do it?

• Communication with ourselves

• Communication with others

How do we do it?• informal techniques

• formal techniques

How effective is it?• different techniques for different purposes

• eg. a road map, an organisation chart, a data flow diagram

Process modelling processes are the “action” part of

businesses process modelling graphically represents

the processes which act on data to • capture• manipulate• store• distribute

Process modelling principal techniques

• functional decomposition• data flow diagrams

associated techniques for modelling the details of low-level processes• structured English• decision tables and decision trees

Data flow diagrams (DFDs) model the flow of data into, through, and

out of an information system represent an information system as a

network of communicating processes• show the processes that change or transform

data• show the movement of data between

processes

18

2

calculateprice

loan application

Products

Suppliers

• process

• data flow

• data store

• source/sink

Components of data flow diagrams

any "real" system is too large to represent as a single data flow diagram

the solution is to decompose the system into a hierarchy of levels of processing

the process model of the system then consists of a set of levelled data flow diagrams

levelling of DFDs improves their readability and usefulness as a communication tool

Levelling Data Flow Diagrams

20

Levelling DFDs

12

3

1.1

1.2

Context diagram

Level zero diagram

Diagram 1 (at level 1)

Data flow diagrams may focus on either:

the “physical” view of the system’s processing

OR the “logical” view of the system’s

processing

Logical and physical DFDs

the data dictionary is a database or repository of information about objects identified during systems development

every object (and each of its components) must have a definition in the data dictionary

the data dictionary is a major source of documentation about the information system

Data Dictionary

the processing that occurs within the bottom level (primitive) processes in DFDs needs to be defined

detailed process descriptions are also known as minispecs

detailed process descriptions form part of the data dictionary: they define the contents of primitive processese.g. Structured English, decision tables, decision trees

Detailed Process Definitions

System designThe main objectives of the design phase are: to provide alternative design solutions to assist in the selection of a design solution to acquire the necessary hardware and software to design and integrate the various physical

system components .. interfaces, security controls, files/databases, etc ...

Systems design features

Design features that lead to more correct systems that are easier to maintain and modify: • Small module size .. easier to write and test, and they are

less likely to affected by change• Modular independence (coupling) .. the less the inside of

one module depends upon another, the easier it will be to test and maintain

• Modular strength (cohesion) .. measures the strength of association of elements within a module

• “black box” characteristics

Documentation• Not necessarily a piece of paper.• Any permanent medium used to communicate to other people

can be classed as documentation• Product and documentation should be developed at the same

time• DOCUMENTATION IS PART OF THE PRODUCT

Documentation is communication:• the objective is to:

• create a specific effect • on particular readers • who want specific information, • have particular characteristics and • will read under particular circumstances.

Presentations person to person communication high credibility single purpose relatively short duration a once-only event no permanent record

Using presentations in systems development reporting an important event or milestone sharing knowledge with your peers responding to a request for information gaining immediate feedback on a proposal requesting approval influencing the audience demonstrating an operational feature

systems development is a team effort teams are organised on a project basis team membership can include:

IT managers, systems analysts, users, business managers, programmers, and other specialists at various points in the project

Teams in systems development

Project manager - manages the project Analysts/designers - the architects who decide

how the system will look and work Programmers/database/network designers - the

builders who make and put together the system components

Operations/systems administration/data communications - the operational people who look after the technology infrastructure to make the system run

Computing People in the SDLC

Senior managers - who decide what the organisation’s needs and priorities are and allocate resources accordingly

Middle managers - who decide how their part of the organisation runs, allocate resources accordingly and advise or seek support from senior management when necessary

End users (operational staff) - who do the work

Business People in the SDLC

The Role of the Systems Analyst to understand the business’s information needs

• what information is needed?• for whom?• in what form?• when?

to describe the business’s information flows to identify problems and opportunities to suggest possible system solutions

Project management: why is it needed? the number of people involved the number of tasks to be done the extent of the interaction between the

tasks and people the complexity of the interactions between

the tasks and people

Basic process of project management

• Select systems development methodology• Plan the project tasks• Estimate the resources and time required to complete

individual phases of the project• Staff the project team• Organise and schedule the project effort(tasks/time/

people/technical resources) and therefore cost• Control the project development (directing the team,

controlling progress, replan, restaff, .... )

Quality in systems development various definitions e.g.

Ability to satisfy stated/implied needs the cost of detecting and correcting errors

rises greatly during the SDLC must be embedded in the systems development

process: product and process implementing quality: e.g. standards, technical

reviews

Types of Information Systems There is a range of information systems to serve

the varied needs of users:• Transaction processing systems • Electronic commerce• Process control systems • Management support systems: Management information

systems, Decision support systems, Executive information systems

• Knowledge-based systems: Expert systems, Neural networks, Robotics

• Multimedia systems• Office automation systems • Geographical information systems

each type of system has its own literature, technology, specialist skills, etc

each type of system is allied with other disciplines

a large and ever-expanding range of specialised software is available for these types of systems

each type of system requires a particular set of technical skills to develop them

different types of system tend to have different types of key users involved in their development

Types of Information Systems