Lecture Outline 11

The Development of Information Systems

Chapter 8 page 390+

SYSTEM DEVELOPMENT

- sometimes, a system that is needed by a business is not available as a 'canned' system which can be bought and installed

- such a system must be custom-built either by systems developers in-house or by external consultants

 

- we now study how a business information system would be built in-house by the Information Systems Department of an Organization

-what kind of system?

- recall Library System

- recall application components:technical components:organizational components:

System Development Life Cycle: *L-- usually a system is developed in specific SDLC stages:

1. System Investigation:a) Problem Definitionb) Feasibility Study

2. System Analysis3. System Design

a) General Designb) Detailed Design

4. System Development (Building)5. System Implementation6. System Maintenance

-Stages not necessarily linear

A LIFE CYCLE OVERVIEW:

System Investigation:<should we really develop a new system?>

- identify problems with the current system and opportunities for improvement- why do we want a new system?

e.g. from Library:

- do initial feasibility study for the proposed system *L

- financial feasibility (is $ available)- technical feasibility (is equipment

available)- operational feasibility (will people be able

to work with new system)

- if we determine that a new system is feasible, we go on to the next stages

System Analysis: *L- analyze the current information system (manual or computerized), in terms of data, processing and information flow, and user input/output

- ask where are problems with the current system or what other reasons are there to develop a new system

-we get an idea of WHAT will be required of the new system in terms of data, processing, and user interfaces; we document this in detail

System Analysis *MC

• We now look at analysis in more detail

• After the preliminary investigation, if the system proposal is found to be feasible, a detailed analysis is carried out– For the current system– For the requirements of the new system

System Analysis (cont’d)

• A systems analyst can use different ways of gathering the information on system features and requirements *L– Current system documentation– Sampling outputs and input forms from

current system– Observation; apprenticing with a user;

videotaping people using the system– Administering questionnaires– Interviewing users

Documenting System Requirements *MC

• What has been discovered through the above techniques needs to be documented adequately

• Can use English descriptions, but then will need to use structured diagrams

• Might use traditional diagrams (data flow diagram and program structure chart)

• OR, may model entire system as a set of interacting objects (OO – object-oriented)

System Design

- h ere we figure ou t in d etail HO W we w ill satisfy the need sof th e n ew system :

- what w ill the screens and rep orts look like?

- how w ill we set u p ou r d ata tables?- what p rograms w ill we n eed to write?- what h ardware w ill we n eed? ... etc.

- we end up w ith a d etailed design ("blueprint") for ou rsystem

System Design *MC

• Detailed design for– Database– Programs– Menu, input, output screens, reports– Controls– Hardware & telecomm– Organizational aspects

Two Ways of Diagramming for Analysis and Design *MC

• 1. The Traditional Structured way– Data and programs designed separately– For data: entity-relationship diagrams

(covered)– For programs:

• Start with data flow diagram in analysis• This becomes the program structure chart in

design

The Data Flow Diagram DFD

• Uses only 4 symbols: – square (external entity)– Curved arrow (data flow)– Open ended rectangle (data store)– Circle (process)

• See handout

Drawing a DFD

• Narrative: an application form comes in from the applicant. It is screened for completeness. If incomplete, it is sent back to the applicant. If complete, it is compared with the latest job requirements list from the personnel file. If the position on the application is vacant, the application is sent to the personnel department after the applicant’s name is recorded on the potential interview list which is kept in a filing cabinet

DFD for the above narrative

• See handout for Diagram

• Be able to describe how a DFD is drawn from a narrative

• You will not be required to draw one

Program Structure Chart

• A hierarchical chart with levels

• Each rectangle is a block of (3GL) program code

• Block below is called by the block above

• See handout for structure chart and the code it represents

Another way of analyzing and describing data and programs

• Object-Oriented Analysis and Design

An Object

• a structure that has BOTH attributes (variables, properties) and programs (methods) that act on these properties

• in an object, the attributes and programs are encapsulated

Example: a Customer Object

• - attributes: customerNo., name, address, phoneNo. creditLimit

• - programs: acceptCustomer(); assignCreditLimit(yearlyEarnings);

deleteCustomer(customerNo)

Object Messages

• An Object Oriented Information system is built in such a way that object send messages to other objects

• A message activates thee execution of a specific program that is contained in the object receiving the message

Prescribed diagrams

- when developing a new system in the object oriented way, the system development team uses specific diagrams in the Unified Modelling Language (UML):

• - use case diagrams (how system will be used)• - object class diagrams• - object interaction (sequence) diagrams

• From these diagrams we will know how to set up our database and how to write the programs for the new system

Design of other system components

• The diagrams helped us to design the database and programs for the new system

• We also have to design: menus, input screens, output screens, reports, system controls, hardware and telecommunication plans, organizational aspects

After system design, *L

• Programmers code programs that belong to each object class

• Programs are tested and loaded onto disk

• Database personnel set up the database on the disk of the server

• System is implemented

• Users are trained

• System is in regular use

System Developm ent

- th e m ain task h ere is choosing a languag e and writingan d testing th e required prog ram s as well as setting up th ed atabase

System Im plementation

- on ce th e system is ready, we in stall it, train th e u sers,an d m ake it p art of regular daily workings

System Maintenance

- h ere, errors are corrected and enh ancements are addedto th e system after it h as b een working for som e tim e

{even tually th e system w ill b ecom e inad equate and we w illcycle b ack to stag e 1}

- th is d evelopment activity is continuous, but sub-dividedin to l ife cycle stages; d ifferent p eople h ave su b-d ivided th eactivities in d ifferen t ways an d there are a number ofd ifferen t l ife cycles b eing taugh t

** think of th e above phases as ap plied to b uilding a n ewschool (som ething tangible) and compare w ith building an ew system

Alternatives to Building a System In-house *MC

• Limited IS Staff

• IS Staff has limited skill set

• IS Staff is overworked

• May take too long