Systems Development Visuals

8/12/2019 Systems Development Visuals

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NCC Education Limited, 2007

Businesses, Systems and Teams - 1.2

V 2. .0

ContentsComputers in the Modern World

Information Systems Velotec Case Study

The Information Systems Department

Velotec Information SystemsRelationships with Business Managers

Overview of System Development Life Cycle

Townsfield Case Study


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V 2. .0

Introduction

Module covers a number of topics involved withcomputer based systems development

Emphasis will be on business use of computers

Knowledge gained will enable you to become ajunior member of a systems development team

A case study approach and exercises will be used toreinforce the topics

The exercises and discussion points will involve allstudents in class discussions

A second case study is provided to enable studentsto consider alternatives


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V 2. .0

Computers in the ModernWorld

Computers are used everywhere

1981 the first IBM PC ran on a 4.77 MHzmicroprocessor

1990 PC became widely used, many applications

available 1987 Internet became commercially available

around 28,000 host computers connected

now we have around 500 millionWe are thus still in the early days of development!


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V 2. .0

Computers in the Modern WorldDiscussion point 1

As a group exercise, discuss how computers affectthe lives of group members

What would change if all computers failed to workfor say one week?

What effect would this scenario have on you, onyour family; on anyone you know who has a job?


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V 2. .0

Computers in the Modern WorldAnswer Discussion point 1

There is no correct answer, the purpose of the discussion is

to raise the groups awareness of the impact computers haveon our daily lives

Each person should determine how their life would change ifall computers failed to work for one week

Most shops which use computerised checkout machineswould shut, banks would have to close, no one couldwithdraw money from their account. Traffic lights and cellphones would cease to work, aircraft could not land or in

some cases, fly safely. Hospital life support machines wouldstop and patients would die

Many many others!


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V 2. .0

Computers in the Modern WorldDiscussion point 2

Discuss some of the good and bad uses ofthe Internet

What will computers be used for in yourlifetime?

Note: as a computing student, you will be partof this development


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V 2. .0

Computers in the Modern WorldAnswer Discussion point 2

Identifying the good and bad uses of the Internet will enableyour group to appreciate that inventions of man are notalways used for peaceful or ethical purposes. Some peopleuse technology to commit crime and to create unsuitablecontent for websites. You will be aware of hacking but thatis a very mild form of bad use compared to some illegal uses

of the Internet

You may wish to debate how this can be stopped orcontrolled

You should also consider what computers might be used forin your l ifetime, for as a computing student, you will be partof this development. Will everything be on the web?


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V 2. .0

Communicating Design

How do we show a user what a computer system

will look like? Like other professions, we use models

Later we look at types of model we can use

First we need to understand a computer systemin business it is usually called an Information

System

the purpose of an IS is to provide information toits users


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V 2. .0

Information Systems A system is a

collection of components- machine, software and humans,which all co-operate in an organised way to achieve somedesired result

M E C Hull, K Jackson, A J J Dick. (2004) Requirements Engineering, Springer ISBN 1-85233-577-7

NOTE the use of quotation marks, hence words not plagiarised

A railway is a system. The components include:

track, signals, drivers, guards, passengers, controls,

finance procedures, ticket sales, timetables,etc it has sub systems, such as track and signal control

systems


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V 2. .0

Information SystemDiscussion Point 3

In groups, identify a typical InformationSystem that you have seen or ideally used inyour daily life

Identify how the IS uses computers for the

benefit of the business and for the customer


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V 2. .0


Could select fast food outlet e.g. McDonalds

typical Information system (IS)

process of collecting data, the procedures andpeople involved, all combining together in astructured way

in a business organisation an IS collects, storesand analyses data to provide information to staff,customers and management


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V 2. .0


What happens when you enter a McDonalds?

What type of data entry keyboard is used andwhy?

How are changes made when new productsare available for sale?

What information is displayed and where?What data is collected and how can this be

used to improve the business?


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V 2. .0


Collects the type and number of each product sold in each 15minute slot of each day

Connects to head office to automatically reorder productsfor next delivery

Store managers can identify: the number of products needed in stock to ensure they do

not run out

number and type of product to be cooked and readynumber of staff required for each period

Analyses sales pattern of new products versus old


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V 2. .0

Velotec - The Business

Medium sized manufacturing and retail

services companyProduces car accessories and tuning

equipment for the enthusiast

Fits new brakes and exhausts via ten drive-inworkshops

Produces high technology components andassemblies for the specialist automotiveindustry


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V 2. .0

VelotecOrganisation

Structure

IS Manager

Chief Accountant

Finance Director

Director Retail Operations

Director Workshop Operations

Director Human Resources

Director Marketing

Manager High Performance Products

Manager Consumer Products Engineering

Director Manufacturing

Managing Director

Company Secretary

Chairman


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V 2. .0

Velotec Major Systems

A recently set up website and the associated

back-end systems

A large stock control system

A customer loyalty scheme based on abudget card

Special purpose engineering analysis

programsSpecial purpose accounts system


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V 2. .0

The Information SystemsDepartment

IS Manager

Operationsmanagement

User supportSystems support

Telecommunications

or networkmanagement

Developmentmanager

Project manager

Systems analystDatabase

administrator

Programmer

Project support


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V 2. .0

Development Project Team Roles - 1 Project manager

takes full responsibi lity for the delivery of a system ontime, on budget and to an agreed quality standard

Systems analyst

defines what a system is required to do in order to meet

the needs of the business

Database administrator

responsible for designing the database so that it is able to

meet performance, security and integration requirements

often continues to provide support after the development

project is completed


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V 2. .0

Development Project Team Roles - 2

Programmers

programmers use their knowledge of a programming language to

implement the system defined by the system specification

large projects often use contract programmers who are hired for their

very detailed knowledge and skill of the particular programming

language and specific development tools

Project support

large projects may also use a number of people to provide support

services to the project teame.g. project l ibrarians, auditors and technical specialists in areas

such as Operational Research (OR)


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V 2. .0

Velotec Information Systems

Started twenty years ago with a combination of anexternal bureau service and a small mainframe thatwas used for accounts and stock control

Replaced by a UNIX based system

Network introduced to allow file and print sharing

The old UNIX system was replaced by more modernUNIX servers and incorporated into the network

As PC power increases, the UNIX system is being

phased out eCommerce being considered


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V 2. .0

Velotec IS DepartmentOrganisation Structure

Secretary

Network

technician (2)

Networkmanager

Help desk

staff (2)

Support

technician (5)

IT supportmanager

Databaseadministrator

Systems

analyst

Programmer

(2+X)

Project

manager

Developmentmanager

IS Manager


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V 2. .0

Many titles over the last 20 years

Computer Department was common

Data Processing (DP) Department

Management Information Systems (MIS) orInformation Systems Department

Ownership of systems moved from IS Department to

business managers

History of the IS Department


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V 2. .0

Historical View of the RelationshipBetween Systems Development

Teams and Business Functions Neither the business manager nor his staff had any real

ownership of the project

the users would often feel that the new system was beingimposed on them by another (the IS) department

the business manager would take no responsibil ity for the

success of the new system, because it was an ISdepartment system, not his


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V 2. .0

A More Modern Approach

Recognises that business systemsshould be owned by business

managers and that ownershipshould extend to thedevelopment process


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V 2. .0

Decision Making Processes - 1

Leading up to a development project

The business manager recognises that an opportunityexists to improve the way his/her department operates, or

that a new requirement exists that requires an IS to

support it A business justification for a new or modified system is

produced and presented to the IS Steering Committee for

approval and for prioritisation as part of the IS Department

workload


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V 2. .0

Decision Making Processes - 2

The IS Department forms a project team which carries out an

initial investigation with the business manager

If an internal development project is undertaken, the

business manager willown the project

take responsibil ity for the implementation of the system

be held to account for the achievement of the expected

business improvement


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V 2. .0

Reasons for Problems - 1 Business managers usually do not understand requirements

The systems analyst may have no previous experience of thebusiness area

The language (not programming language) needed to define a

specification is usually very obscure from the businessmanagers perspective

The business managers requirements usually result in

changes to the requirements specification

S


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V 2. .0

Reasons for Problems - 2

Some system development life cycle models require the full

requirements specif ication to be completed before work startson system design and implementation

We expect systems to be user-friendly, but this quality isextremely diff icult to define and to specify

Is there a solution ?

We will see later in the module how we try to produce modelsof the system which business managers can understand

B i S t d T 1 30


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V 2. .0

Do this

withSkill A

Then this

withSkil l B

Then this

withSkill C

Then this

withSkill D

Pass all results to the next phase

Start

Finish

Linear Life Cycle Model

Businesses Systems and Teams 1 31


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V 2. .0

System Maintenance

DevelopMaintain

Phase

outResources

Time

Businesses Systems and Teams - 1 32


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V 2. .0

Maintenance Work Categories Corrective

putting right any errors that remain in the system

Perfective

improving the system so that it better meets the needs of

the business

Adaptive

changes that are needed because the organisation orperhaps legislation has changed

Businesses Systems and Teams - 1 33


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Businesses, Systems and Teams 1.33

V 2. .0

Velotec System Maintenance

No separate maintenance function within

the IS Department

All maintenance work is undertaken byfull-time programmers and contractors

Corrective maintenance is prioritised onthe basis of the seriousness of theproblem



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, y

V 2. .0

A Maintainable System

Should have a well defined developmentmethodology

Is fully documented

Conforms to good programmingstandards

Has been tested effectively



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y

V 2. .0

Summary The development of large business systems is always a collaborative

effort, needing

a combination of ski lls and experience that no one individual is likelyto possess

a sufficiently large resource to be able to complete a project beforethe business needs change and to contribute to the business

We have emphasised

the main skills and functions that typically comprise an IS projectdevelopment organisation structure

that successful projects are owned by the business function thatcommissions them

that the need for collaboration between the IS specialists and users isa key requirement for success

that the development process may not be the most costly part of thelife cycle of a system


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NCC Education Limited, 2007V 2. .0

Townsfield Soft Drinks Co. - 2

The data collected via the terminal includes the

number of units sold for each product, and themoney taken

This data is analysed to identifystock sold and which therefore needs replacing

performance of each outlet against expected sales

trends in sales of products

income against predictions and business efficiency

reports produced for each director


T fi ld S ft D i k C


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Townsfield Soft Drinks Co.

Exercise 1

Bearing in mind the type of business, would it be

useful to collect the date and time of each sale?

Could this extra data be used to provide useful

information to local and senior management?

Is there any advantage to be gained by transmittingthe data directly to HQ as it is collected at theterminal?


Townsfield Soft Drinks Co


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Answer Exercise 1

Some useful information would include:

Collecting this data would enable an analysis to identify busy andslack periods in order to facilitate more accurate scheduling of staffand assist in establishing the loss of income if the opening times ofthe outlet were changed. (Identify operating costs per hour againstincome per hour)

Transmitting the data directly as it is collected would provide aninstant analysis, and ensure data is not lost if for any reason theterminal fails, is damaged or destroyed in a fire. However there wouldbe a cost associated with having communication lines permanently

connected between HQ and each of the 200 outlets.

YOU should think of more benefits!




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Business Review

Old computer system run by IT Department

Business reorganised, Director for each division

Objective placed on profit, identified by

customer

product Four key databases identified and set up

financial

retailwholesale

HR




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IT support

Consultants used to identify how IT could support

reorganised businessConsultant report useless

A new consultant advised

TO PLACE CONTROL OF IT with USERSAll IS systems to be controlled at board level

All projects reviewed by Company Steering

Committee consisting of all 6 board directors



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Townsfield Soft Drinks Co.Company Steering Committee

CSC considers projects on basis of

what advantage will be gained by the business?

what will the business lose if it does not

implement the proposed project?what information do we need this project to

provide?

will it be cost effective?CSC then approves best; achievable within resource

base



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Townsfield Soft Drinks Co.Company Steering Committee

CSC meets every 2 months to

Review current project progress

Review list of projects

Consider new projectsgiven business needs may change over time

external factors cause change

Ad hoc projects- minor changes possible with anyboard member signed approval

(Effect of ad hoc projects discussed later)



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Townsfield Soft Drinks Co.Exercise 2

In groups, students should discuss theinternal and external changes which are likelyto affect a business

Students should select a business they usethemselves and hence know about



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Townsfield Soft Drinks Co.Answer Exercise 2

Depending on the type of business selected,ideas may include; new chief executive withdifferent ideas for the companys future,takeover by a rival company, price changesand delivery issues with raw materials, effectof competitors entering or leaving the market,government tax or other business legislation

changes, population change, staff changes,loss of particular expertise



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Townsfield Soft Drinks Co.CSC

Project delay may be due to too many ad hoc

projects

board will require person who signed approval, to

justify to the board (removes blame from IT

section)

Is this an improvement on Velotec project

developments?



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Townsfield Soft Drinks Co.External Data

External data bought in from specialist

organisations, for example:

demographics; population changes due to births, deaths,

plans for new house building, developments in

workplaces (expansion or reduction)weather, history and predictions

major sporting and other large events

These all have an effect on sales



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Townsfield Soft Drinks Co.Business Change

Customer needed more responsive delivery

So to retain customers:

improved order system

improved stock controlnew warehouse locations

IT section unable to provide in time for business

needs External package bought, modified by contract staff



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Townsfield Soft Drinks Co.Exercise 3

In groups, students should discuss how vital the

use of IT is to this business

could the business manage without IT?

briefly explain what the impact of no IT would be

Could Townsfield use IT in other areas of itsbusiness?



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Townsfield Soft Drinks Co.Answer Exercise 3

The main purpose of this exercise is to establish how wellstudents understand the use of IT within a business and

appreciate that having implemented IT systems it is, for mostbusiness organisations, impossible to return to manualsystems

Clearly, having implemented a system linking outlets to HQand with computerised stock control, it would be impossible

to manage the business without IT Townsfield have their own outlets linked to the head off ice

system for stock replenishment, they could have allcustomers linked directly to the head off ice system. Are

there delivery vans linked to a GPS (Global Satelli te System)so that they can be tracked and diverted by HQ if necessary?Do the delivery vans carry web enabled portable devices sothat all deliveries they make can be instantly uploaded to theHQ system?

Mathematics for Computing - 2.1


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NCC Education Limited, 2007V2 . 0

1

International Diploma in

Computer Studies

Systems Development

Mathematics for Computing



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2

ContentsNumber systems

Introduction to numberbase conversions

Non-decimalconversions

Arithmetic calculations

Data structures

Check digits

Statistics

Measures of spread ordispersion

Elementary probability



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3

Introduction

Members of systems development teams need to be

numeratesystems analysts, programmers and project

managers

The purpose of this chapter is to ensure that youhave the appropriate level of mathematicalknowledge to enable you to progress with the

courseA range of topics will be covered to just sufficient

depth to be useful, but no further



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4

Number Systems

DecimalBinary

Octal

Hexadecimal

Fractions and decimals



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5

Number BasesNumber system Decimal Binary Octal HexadecimalBase 10 2 8 16Digits available

0 0 0 01 1 1 12 2 23 3 34 4 45 5 56 6 67 7 78 89 9

A

BCDEF

In the case of the decimal system, this base is 10since there are ten different symbols used to show

quantities in that system (0 to 9)

Each number system has

a base, which indicates

the number of differentsymbols used in that

system



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6

Decimal

Hundreds Tens Units

102

101

100

2 5 8

10 is the base of the decimal system

Place values in the decimal system, move right to leftof a whole number

For number 258, the place value of 5 is tens i.e. 5 x 10

=50


Binary


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7

BinaryPowers of 2 2

5 2

4 2

3 2

2 2

1 2

0

Positional value 32 16 8 4 2 1

1 1 0 1 0 1

The base of the binary system is 2

The table above shows the meaning of the binary value 1110101

Multiplying positional values by the binary values and adding them

up:

1 x 32= 32 1 x 4 = 4

1 x 16 = 16 0 x 2 = 0

0 x 8 = 0 1 x 1 = 1

So if the number 53 was stored in a numeric form internally in a

computer, it would be stored as binary value 110101


Octal


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8

Powers of 8 84 83 82 81 80

Positional

value

4096 512 64 8 1

3 0 5 6

Multiplying values and adding them up

3 x 512 = 1536

0 x 64 = 0

5 x 8 = 406 x 1 = 6

Decimal total 1582

The table below shows how an octal value of 3056 would berepresented



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9

Hexadecimal

Powers of 16 163 162 161 160

Positional value 4096 256 16 1

2 F A 6

Multiplying values and adding them up:

2 x 4096 = 8192

F(15) x 256 = 3840

A(10) x 16 = 160

6 x 1 = 6

Total 12198



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Fractions and Decimals - 1

Multiplying values and adding them up:3 x 10 = 30

6 x 1 = 6

5 x 0.1 = 0.5

2 x 0.01 = 0.028 x 0.001 = 0.008

Total = 36.528

Powers of 10 103 102 101 100

. 10-1 10-2 10-3

Positional value 1000 100 10 1 0.1 0.01 0.001

3 6 5 2 8



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Powers of 2 23 22 21 20

. 2-1 2-2 2-3

Positional value 8 4 2 1 0.5 0.25 0.125

1 0 1 0 1 1

Multiplying values and adding them up:

1 x 4 = 4

0 x 2 = 0

1 x 1 = 1

0 x 0.5 = 01 x 0.25 = 0.25

1 x 0.125 = 0.125

Total = 5.375

Fractions and Decimals - 2



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12

Quotient Divide by Result Remainder

117 2 58 1

58 2 29 0

29 2 14 1

14 2 7 0

7 2 3 1

3 2 1 1

1 2 0 1

Reading the remainder column from the bottom up we see

that 117 Decimal =1110101 Binary

Decimal to Binary



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Decimal to Octal

Quotient Divide by Result Remainder 236 8 29 4

29 8 3 5

3 8 0 3

The result is 354, reading the remainder column inreverse



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Quotient Divide by Result Remainder

473 16 29 9

29 16 1 D

1 16 0 1

The result is 1D9, reading the remainder column in

reverse

Decimal to Hexadecimal



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Binary to Octal

Binary 000 001 010 011 100 101 110 111

Octal 0 1 2 3 4 5 6 7

The table can be used to do rapid conversions

from binary to octal



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Octal to Binary The process is the reverse of binary to octal and you can use

the same table

Any unnecessary zeros can be removed. For example:

Octal 2 7 4 3

Binary 010 111 100 011

The left hand zero is not needed, so we are left with

10111100011



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Binary to Hexadecimal look up tableBinary Hexadecimal Binary Hexadecimal

0000 0 1000 8

0001 1 1001 9

0010 2 1010 A

0011 3 1011 B

0100 4 1100 C

0101 5 1101 D

0110 6 1110 E

0111 7 1111 F

Split binary numbers into groups of four digits (24 = 16 which is the

hexadecimal base), zeros may be added if necessary

Binary 0110 1011 1011

Hexadecimal 6 B B

Notice that the leftmost group was padded on the left with an extra zero



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Hexadecimal to Binary

This reverses the previous process, just as

we saw with Octal to Binary conversions

For example:

Hexadecimal 9 A C

Binary 1001 1010 1100



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19

Binary Addition

Rules of binary addition

0 plus 0 produces 0

0 plus 1 produces 1

1 plus 1 produces 0 with

a carry of 1 into the next

most significant place

Look up tables make lifeeasier and less mistakes!

Decimal Binary

0 0

1 1

2 10

3 11

4 100

5 101

6 110

7 111


Data Structures- Memory


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Data Structures MemoryOrganisation

13 2AF 1 00 3 19 4 D4 5 00 6 00 7 11 8 C6 9 00 A 89 B 12 C

AF 1Address

Content



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Arrays

An array is a series of individually numbered

elements e.g T 3,4 or customer 7,15

An element is single unit of data, such as aninteger or a character

All the elements in an array are of the sametype



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Two Dimensional Arrays

3,43,33,23,13,0

2,42,32,22,12,0

1,41,31,21,11,0

0,40,30,20,10,0


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24

Queue

Head (remove)

Tail (add)


Check Digit Calculation


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25

Check Digit Calculation

Check digits used to detect errors at data entry

The modulus 11 check digit system is one of the most

popular methods for calculating check digits Choose a random number weight the same length as the

number to be checked

Multiply the matching digits in the random number and the

entered number Add up all the numbers resulting from the multiplications

Divide the sum by 11, recording the remainder, if any

Subtract the remainder from 11; this is the check digit soappend it to the end of the number



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26

The Mean - 1 Eight numbers: 7, 21, 13, 17, 23, 18, 9, 20

Add them up (giving 128)

Then divide the total by the number of items (8), giving the mean of 16

This particular average can only be used with data which is quantitative

Note that the presence of even one value which is disproportionate to theothers may easily distort the value of the mean - for example if theoriginal set of values contained the 12 numbers:

3, 3, 4, 4, 4, 4, 5, 5, 6, 6, 6, 176

The mean would be the total (226) divided by the number of items (12)giving 18.83, which is not typical of the majority of the numbers


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The Median Example: Take 14 values, arranged in order of magnitude:

10900 11600 12500 12700 13400 13800 14100 15700 16200

17200 17700 17800 18700 19000 The median is way, i.e. between 7th and 8th value

(14100 + 15700) = 14900, which is more easily found thanthe mean and it is not so affected by extreme values

The median of the seven items below, is 8:3 4 7 8 12 15 8164

it is exactly the same as the median of the seven items:3 4 7 8 12 15 17

Disadvantage is that the value of the median does not at allreflect the values of anything but the middle term(s) in adata set, whereas the mean is affected by each value



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29

Language Used Frequency

FORTRAN

C

JAVA

VISUAL BASIC

C++

SQL

24

43

8

16

14

1

The Mode The mode is defined to be the

value which appears mostcommonly in a list of data items

especially well suited to data

which is qualitative

In the table shown, the popularityof a number of different

programming languages wasinvestigated

if two values appear with equal

frequency, both are classified as

the modes and the distribution is

referred to as bimodal

Ease of determination - may beused for planning purposes

The mode is therefore C



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30

Frequency Distribution

Frequency Distribution of RepeatPurchases with a Loyalty Card

0

20

40

60

80

0 1 2 3 4 5 6 7 8


Relative Frequency Distribution of PC Ages


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31

RelativeFrequency

Distribution0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

1 2 3 4 5 6

Department A

Department B

Age of PC 1 2 3 4 5 6 Total

Department A 16 10 8 4 2 1 41

Relative Frequency 0.39 0.24 0.20 0.10 0.05 0.02 1

Department B 5 3 3 3 2 1 17

Relative Frequency 0.29 0.18 0.18 0.18 0.12 0.06 1



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32

Measures of Spread

2 4 6 8 10 12 14 16 18 20

A

D0

0.5

1

1.5

2

2.5

3

Three Frequency Distributions

A

B

C

D



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Distribution RangeA 6

B 6

C 14D 6

The Range The range is the

simplest measure ofdispersion

found for any distribution

by subtracting the

smallest data value in thedistribution from the

largest



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Standard Deviation The features that we require of a good measure of dispersion

are

that every data value is taken into account that data values are weighted according to their

frequency

The standard deviation satisfies these criteria. Inmathematical terms this is shown as:

=

n

i

i

n

xx

1

2

1

)(



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Probabilities - Definitions Sample space the sample space is defined as the

set of all possible outcomes of an experiment

Event each possible outcome of an experiment isa sample point; a collection of sample points with acommon property is an event

Probability the probability of a sample point is theproportion of occurrences of the sample point in a

long series of experiments


Relative Frequency


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Definitions and Probability

Relative frequency measures the way in which oneparticular category occupies the distribution as awhole and in what proportion

ExampleHow likely is it, that a piece of equipment chosen at

random from Workshop W8, will be between 4 and 5 years

old?

We could view the result as a measure of the probability

that the age of the equipment lies between those limits


S


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37

SummaryWe have covered a range of basic mathematical

techniques The ability to use and understand numbers in any of

the common bases such as decimal, binary, octaland hexadecimal is frequently needed in systemdevelopment activities

There are other mathematical topics, for examplesets, logic, and particularly for graphics, matrix

manipulation. These topics are not required at thelevel of study for this module

System Development Life Cycles - 3.1


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NCC Education Limited, 2007V2.0


Computer Studies

Systems Development

System Development Life Cycles


C t t


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Contents Software engineering

Project stages andproject control

The Waterfall li fe cycle

model The V model

Velotec training systemhistory

Prototyping

Velotec product datamanagement system

Rapid application

development The Spiral life cycle

model


I t d ti


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Introduction

This chapter will give a brief overview of:

history of software development leading to i t becoming an

engineering discipline

size and complexity issues

quality and productivity

Project stages and control

System Development Life Cycles (SDLC)


S ft E i i


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Software EngineeringSoftware engineering originated in 1968

in response to the software crisis

Need to regard software development assoftware engineering (disciplined andstructured)

Regarding software development as acraft causes problems


S ft E i i


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Software EngineeringDefinitions Software engineering is an engineering discipline,

using a systematic and organised approach(including theories, methods and tools) which isconcerned with all aspects of software productionfrom the early stages of systems specificationthrough to maintaining the system after it has goneinto use

Source: Ian Sommerville (2006) Software Engineering 8th Ed,Addison Wesley ISBN - 0321313798


Prod cing Soft are is Diffic lt


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Producing Software is Difficult Large software systems are the most complex products that

man has ever produced

Some of the most complex products include ships, largeaircraft, cars, worlds tallest buildings, worlds longestbridges

Small increases in the complexity of a system can mean thediff iculty of production increases almost vertically

Software is intangible (cannot see it)

Software is not subject to well-understood physical laws


System Complexity


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Difficulty

ofproduc

tion

Complexity of product

System Complexity


Size is Important


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Size is ImportantReasons why scaling does not work:

The complexity of a computer system does notincrease linearly with size measured in lines ofprogram code

The idea that adding more resources to a projectwil l allow it to be completed more quickly seems

reasonable in fact adding resources to a project in order to reduce the time needed for

completion usually has exactly the opposite effect - it extends the entire

project duration


Quality


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QualityWe expect that a consumer durable ( razor, hairdryer,

cell phone, TV, car etc) from a well-known supplier

will function well for its entire lifespan

Unfortunately, this is not the normal expectation for

softwareRecall the many software failures you read about

The level of quality we obtain from software productsis not the same as we expect from other products

Why is this?


Productivity


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Productivity Productivity is the amount of useful output

produced per hour

The productivity of two people using the same toolsand process is often quite different

Studies of programmer productivity (same taskswith the same tools) showed a variation between

programmers of at least 16:1Would any other industry accept such a large variation?


Programmer Productivity


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Programmer Productivity Studies of activity vary from one organisation to

another; the following was not unusual:

Programming 13%

Reading programs and manuals 16%Job communication 32%

Personal 13%

Miscellaneous 15%

Training 6%

Mail 5%


Project Stages and Project

Control


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ControlBrief Overview of Stages

Strategic study Business study

Feasibility study

Requirements analysisRequirements

specification

Logical systemsspecifications

Logical design Physical design

Coding

Testing Implementation

Maintenance

Phase out


The Waterfall Life Cycle


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The Waterfall Life CycleRequirements

Analysis

Requirements

Specification

System Design

Code and Test

Maintenance

Implement


The Waterfall Life Cycle -Assumptions


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The Waterfall Life Cycle -Assumptions

It is possible to divide project activities intodiscrete, isolated stages

Each stage is completed before the next one isstarted

Each stage relies on the information produced bythe previous stage, and only on that stage

A project plan can be constructed, based on

milestones, represented by the completion of eachstage


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Velotec Training SystemHistory


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History

Staff need correct training and their skills need to be

monitored; for review against any potential newproject

All training organised by Human Resources (HR)

and carried out by specialist training companiesHR Director commissioned a training tracking

system

Two major issuesDynamic requirements

Reluctance to accept design


Benefits of Prototypes


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Benefits of Prototypes

Any misunderstanding between business managers

and analysts quickly resolved

Make an ideal tool for defining and discussing user

interaction

Easier to understand from users view point

Easier to create


Drawbacks of Prototypes


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Drawbacks of Prototypes Business managers may not understand the

purpose of a prototype

Some prototypes are so realistic that they give theimpression that the project is almost finished whilststill at the systems analysis stage

The effort required to produce a prototype may leadto the development team using it as a part of thenew system


Velotec Product DataManagement System


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Management System

Case Study:High performance products division had

a major problem with parts produced for

motor racing teamCommissioned a system

V Model used by systems development

There were significant problems with thefinished system


Initial Strategy

Iterative Development


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Systems Analysis

Requirements Analysis

Initial Strategy

Feasibili ty StudyReview

Maintenance

Implementation

Testing

Development

Design

Specification


Rapid Development

Requirements


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Code

Integrationtest

Unit test

Design

Prototype

analysis & spec.

System &acceptance test


Create

Agree schedule Identify functionalprototype

FeasibilityBusiness study

DSDM


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Implement

Userapproval &userguidelines

Train users

Review

designprototype

Design and Build

Iteration

Createfunctionalprototype

p yp

Agreeschedule

yReviewbusiness

Identifydesignprototypes

Reviewprototype

Create

designprototype

Implementation

FunctionalModel

Iteration

.

2

1

3

1

23

2


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Summary

Software life cycle development models have been examined


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Software life cycle development models have been examined

Two case studies used to illustrate the problems of theWaterfall model

Introduced the ideas of prototyping and iterative

development

Introduced two alternative life cycles, DSDM and the Spiralli fe cycle, used to demonstrate there are many alternatives

and in many organisations no standard is used, while inothers a standard is adopted, but does not always meet thedemands of the project

Software Analysis and Design Methods - 4.1



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NCC Education Limited, 2007V 2 .0

International Diploma inComputer Studies

Systems Development

Software Analysis and Design Methods


Contents

Analysis and design methods


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Analysis and design methods

Modelling techniques

A history of methods at Velotec

Some traditional methods

Object technology

Program specification


IntroductionS f i i f


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Software engineering attempts to turn a craftdiscipline into an engineering discipline

Need for a software development life cycle

SDLC provides a framework for development

The heart of the development process is theanalysis and design of applications


Analysis and Design Methods


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y gAnalysis methods are those that we use during the

requirements analysis and requirements definitionstages

where we try to discover exactly what is required by the

user

Design methods are used during the system designstage and are closely aligned with the coding

activity that follows

where we use structured methods and produce models


Choosing the Correct Method

Guidelines:


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Guidelines:

Look for a method that is widely used

Look for a method that is adopted by governmentsand other important organisations

Look for a method that is freely available, notproprietary

Look for a method that reflects modern thinking

about life cycles and suits the organisation


Bohm and Jacopini*

Every possible system and every possible


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Every possible system and every possibleprogram requires only the following three

types of construction:Sequencing

Selection

Iteration

*Bohm C and Jacopini G "Flow Diagrams, TuringMachines and Languages with Only Two FormationRules Communications of the ACM (1966)


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Data Model


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Book

Borrower Author

Crows foot One relationship

Crows foot, manyrelationships


Data Flow Diagrams


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Data Flow Diagrams show how data moves

within a system and where it is storedOne of the first types of models to be widely

used

Now a fundamental building block of manyanalysis and design methodologies

Comment on how easy to understand you

find the following models


Person Apply for membershipDFD


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Completedapplication form

Person Apply for membership

Librarian

Member

Membership cardReception desk1

Change memberdetails

2

Delete memberdetails

3

LibrarianDetail changes

Member

Member left

M1 Member f ile

M1 Member file

Application form

Producemembership card


Context Diagram


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Supplier

Chief l ibrarian

Member

Book processing

Delivery

New bookorders

Reservesbook

Returnsbook

Borrows

bookJoinslibrary

List of old books


Decomposition of DFDContextdi


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Further detail

Lowest level DFD

Expands into

is supported by

diagram

Expands into

Mini-spec


Lib B k

Entity Life History


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Library Book

Acquire Available Remove

Buy Gift Loan

Issue Return

Sell Scrapo o * o o

Sequences are represented by boxes

read left to right on the same level

Al ternatives are marked with a small o

in the top right hand corner of the boxRepetitions are marked wi th a small *

in the top right hand corner of a box


A History of Methods at

VelotecMost projects have not used any recognised


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p j y gmethodology, relying entirely on the person

developing the project

Velotec has used some techniques asdescribed in recognised methodologies, suchas Data Flow Diagrams

Previous IS managers thought methodologieswere a waste of time


Structured Systems Analysis


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Attempts at structure led to varioustechniques, including:

Data flow diagramsData dictionary

Decision tables and decision trees

Structured English and pseudocodeNormalisation of data


Jackson Structured

Programming (JSP)S 1 d l h bl b d fi i h i


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Stage 1 model the problem by defining the inputand output data structures, using the tree-likestructure used in the ELH

Stage 2 transform the input/output models into astructural model for the whole system by looking forpoints of correspondence between items in theinput and output structures

Stage 3 expand the structural model into adetailed design model that specifies all theoperations needed for the complete system


SSADM

A variety of techniques are used including

entity l ife histories using a Jackson-like notation


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entity l ife histories using a Jackson like notation

data modelling based on an entity relationship approach

data flow modelling

data normalisation

One of the most highly developed conventionalanalysis and design methodologies

A well-proven methodology that is freely availableand openly documented, used by many governmentdepartments for all projects


Object TechnologyBecame popular in the early 1990s


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Became popular in the early 1990s

Has influenced much thinking about systemsanalysis and design

Has resulted in:

- Object Oriented Programming (OOP)- Object Oriented Analysis and Design (OOA

and OOD)

- Object Databases etc


Attributes of an Object - 1 Encapsulation


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an object packages together data and the access methods

to that data the data within an object can only be changed by using

these methods

the object effectively hides the data from the outside worldMessages

the only way that an object can communicate is by means

of a message

a message can be passed between two objects and may

result in the object carrying out one of its methods


Attributes of an Object - 2 Inheritance


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an object belongs to a class of objects that share the same methods

a new class can be defined that inherits the data structure andmethods of its parent class

the new class can override some of the methods of the parent class

and add new methods

inheritance from a single class can be further elaborated toinheritance from multiple classes

Polymorphism a word of Greek origin, meaningmany shapes in object technology terms, classes that are different can implement

the same message


Object Oriented Analysis and

Design


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Based on objects

Does not mean a total break with the existingstructured analysis and designmethodologies

The Unified Modelling Language (UML) hasgained a lot of acceptance


PseudocodeDO WHILE there are more text records


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DO WHILE there are more words in the text record

extract the next text wordsearch the word table for the extracted word

IF the extracted word is found

increment the words occurrence count

ELSE

insert the extracted word into the tableENDIF

increment the words-processed count

ENDDO at the end of the next record

read the next text recordENDDO when all text records have been read

Display the table


Structure DiagramProduce

invoice


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invoice

Write title

Produce

invoice

body

Write

footer

Write itemdescription

Calculate

tax

Write

value

*Calculateinvoice

line


Start

Locate library

A process is

shown as a box

Flowchart


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Fine? Processfine

No

Yes

y

member

Process

book returned

Another

book?

End

NoYes

shown as a box

A decision isshown as a

diamond

The flow of

processing is

shown as arrows

linking the

symbols


Decision TablesA decision is represented


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A decision is represented

in a flowchart by the diamond symbol

in pseudocode by the IF ... ELSE statement

In a decision table, the question is asked firstfollowed by the answer

either Yes or No


Decision Table - Four BasicElements


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The condition stub

The condition entryThe action stub

The action entry


Rules 21 3 4 5 6 7 8Decision Table


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YCreditworthy?

Salaried?

Reject

Accept

-

-

-

N

Special person?

Y

Y N N N

Y Y Y

Y Y Y N N N N

N N NN

Y Y Y

-----


Simplified Decision Table


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Creditworthy?

Salaried?

Reject

Accept

N

Special person? N

-

N

ELSE

-

-

-


Decision Tables - Useful

FeaturesSimple - easy for the user to understand


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Simple easy for the user to understand

Complete and unambiguous - the analyst cancalculate the exact theoretical number ofrules to be specified

Statements of policy - they say nothing abouthow the policy is carried out

Working documents - like all good analysis

tools, the decision table is a useful workingdocument


Summary

Notations, methods and methodologies forsystems analysis and design


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some notations such as simple flowcharts now

rarely used

other methods have matured and been put to use

in coherent methodologies

Everybody should be using an appropriate

methodology to suit their softwaredevelopment projects


Answer 4.1 - Exhaust Fitting

Context DiagramStock


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Warehouse

Head Office

Customer

Operate workshop

Delivery

Order parts

Stockresponse

Requestswork

Pays for workStockquery

Sales returns

HR Department

Training request

Certi fied fitters


Answer 4.2 - ExhaustComponent ELH


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Exhaust Part

Receive Inspect Use

Accept Return

o o Scrap Returno o

Fit o

Documentation and Standards - 5.1



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NCC Education Limited, 2007V2 .0

Computer Studies

Systems Development

Documentation and Standards


Contents

The need for standards


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Standards and quality

Documentation and codingstandards

Types of documentation


Introduction

The purpose of this chapter is to show that there is much tobe gained from good documentation and compliance with


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be gained from good documentation and compliance with

appropriate standards

We have shown that by far the largest proportion of the lifecycle costs of a system can be absorbed in maintenance,

and that using appropriate standards and documentation is agood way to minimise those costs

In this chapter we wil l take these ideas and apply them morewidely, so that we can see how standards and documentationbenefit us all the way through the development life cycle


Standards

Used throughout the world


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Some examples are:the traffic light system

PC operating systemsfood standards

Can you think of any standardswhich apply to you?


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Standards and Quality

In order to improve quality we have first toha e a process that is ell eno gh defined to


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have a process that is well enough defined tobe repeatable and susceptible to monitoring

A standard provides the framework for this

repeatabilityThis is one of the reasons why written

procedures form part of Quality ManagementSystems


Good DocumentationAccessible


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Readable

Understandable

Correct

Controlled


Accessible

Documents need:


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Documents need:

a clear structure

a table of contents

a detailed indexpointers to other relevant documents

to be catalogued


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Correct


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Documentation should be subject to the fullverification and validation processis this the right thing to document?

is this documentation correct?

Correctness requires testing by means ofpeer review


Controlled

All the products of the software development lifecycle are subject to change, and this includes


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cycle are subject to change, and this includes

documentation Version control systems possess some features

that help to keep control over project products

a check in/check out facili tya baseline and release control capabili ty

the abil ity to create branches in the line of development

A system that does all this can be very complex,but it is necessary to maintain control ifdocumentation is to remain useful


Understandable

Documentation is intended to convey information

It can only do this if the reader is able to comprehend the


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text

Comprehension is based partly on style, but also on theassumptions made by the author about the expertise and

experience of the user

The writer should have a very clear idea about what can beassumed of the reader

Advisable to ask someone to proof read the document


Coding Standards - 1

Coding standards define rules that a


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programmer must follow

Using coding standards helps to produce code

that will be efficient, effective, easy to maintainand understandable by another programmer!

Internal standards usually define other aspectsof a programmer's work


Coding Standards - 2

Function per page, single entry/exit point


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Restrict scope of variables Restrict use of some code statements Standard for variable names uses date for calendar

date, not fruit date!! Never allow pet names or

family names

Use in-line comments to explain code


Types of Documentation - 1

Type Use Stage

Project Initiation

Document

Define scope of project FS, BS


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End of Stage Report Defines the status of developmentat the end of a project stage

FS - I

Data Flow Diagram Define processes and flows of data FS, RA, RS,

LSS, LD

Entity Life History How an entity changes over time FS, RA, RS,LSS, LD

Logical Data Model Relationships between entities FS, RA, RS,

LSS, LD

Flow Chart Show logic of system RA, PD(if at all)

Structure Diagram Shows the processing done by a program LD


Types of Documentation - 2

Decision Table Define complex logic LD

Program Listing Documents a program C

Type Use Stage


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Test Report Summarises testing results TTest Plan Describes how and what will be tested T

Test Case Describes a particular test T

Test Data Defines the data to be used with a test case T

Modification History Tracks changes to a system MUser Manual Describes how to use a system from users

perspective

I

System Manual Describes the operation of a system from a

technical viewpoint

M

Release Notes Describes what has changed since the last release

and any special installation requirementsI, M


Summary

Ensure you fully understand the purposes of


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notations, methods and methodologies forsystems analysis and design

ask yourself, who benefits from their use?

Every organisation should use an appropriatemethodology to suit their softwaredevelopment projects

Testing - 6.1



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Systems Development

Testing

Testing - 6.2

Contents

Defining testing


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Types of testing

Designing and implementing tests

Planning and managing tests

Velotec testing

Testing - 6.3

Introduction

Testing is important you would hope any train, car or plane you use has been thoroughly

tested; increasingly software is controlling such vehicles


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Why and when should you test?

What should you expect to achieve as a result oftesting?

How do you plan, what do you test and for howlong?

We will consider some of the issues involved withserious testing problems

Testing - 6.4

Defining Testing

The average persons definition:

testing makes products work and adds quality to them


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Other definitions include: testing is the process of demonstrating that errors are not

present

testing shows that a program performs its intendedfunctions correctly

testing is the process of establishing confidence that a

program does what it is supposed to do

These definitions are all flawed in quite a seriousway

Testing - 6.5

Testing or V and V

When you read text books on testing you will find thatverification and validation is the name given to the checkingand analysis processes that ensure the software conforms to


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its specification and meets the needs (requirements) of thecustomer. The difference between validation andverif ication was expressed by Boehm (1979). Sommerville*

Validation are we building the right product?

Verification are we building the product right?

* Software Engineering, Ian Sommervil le, Addison Wesley ISBN 0 201 39815

Testing - 6.6

Testing

Testing increases reliability, or suitability forpurpose


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The process of testing is costly

Discovering and rectifying errors

Objective of testing is to find the most costeffective tests available to uncover errors in a

system

Testing - 6.7

What is a Good Test?


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A successful test is one that finds anew error

A good test is one that has a highprobability of finding a new error

Testing - 6.8

Types of Error

Difficult to recognise

Not uncommon for suppliers of bespoke software


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and customer to resort to l itigation

In order to define an error you need to know what

the system is supposed to do (specification)

Important that specifications are produced whichenable the design of tests to explore (use all)

programme code

Testing - 6.9

The V Model

Maintenance

Initial concept

Requirements definition


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Tested modules

System design

Requirementsspecification

Acceptance test

Testedsystem

Integration and test

Code and unit test

Software design

Detailed design

Tested software

Tested system

Tested software

Testedmodules

Module design


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Testing - 6.11

We Cannot Test Everything

Would take too long if for example, Microsoft fully tested each new Windows

l ld th t t th k t?


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release, would they ever get to the market?Too expensive

Labour intensive - good tests cannot be

automatedReal situation

warship test of software controlled torpedo

Testing - 6.12

Probability of Further Errors

errors


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Errors already found

Probability

offurthere

Testing - 6.13

Types of Testing

Black box testing

White box testing

Testing through thelife cycle unit


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package

integration

code inspection

system testing acceptance testing

beta testing

usability testing

conformance testing

Testing - 6.14

Black Box Testing(cannot see inside)

Data-driven

Input/output

F ti l


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Functional

No knowledge of systeminternals

Tests use only standardinput interfaces ?

Testing - 6.15

White Box Testing(can see inside)

Logic-driven

Structural

Glass box


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Glass box

Complete knowledge ofinternals

Tests can use specialinterfaces

Testing - 6.16

Types of System Testing

Used to discovermismatches between thesystem specification and thesystem actually produced

Functional testing

Volume testing

Stress testing


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system actually produced

There are a number of

different types of systemtests that can be used tohighlight specific types oferror

Stress testing Usabili ty testing

Security testing

Performance testing

Documentation testing

Testing - 6.17

Acceptance Testing

A form of black box testing

Critical difference is that it is normally carriedb h f h


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Critical difference is that it is normally carriedout by the customer or user of the system

Completion of acceptance testing is usually atrigger for a major stage payment and sign off

Often carried out using a previously defined

test plan and test cases

Testing - 6.18

Beta Testing

Copies of system released to trusted usersunder a non-disclosure agreement


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Intended to supplement and follow on fromfull internal system testing designed to

uncover errors in field use of the system

Should never be a replacement for thoroughsystem testing

Testing - 6.19

Usability Testing

Investigates how easy a new system is to use

Determines whether the system behaves in an

acceptable way for specific types of user/specific


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acceptable way for specific types of user/specifictasks

Points to be considered are:ease of learning

ease of use

flexibilityattitude

Testing - 6.20

Conformance Testing

Testing of hardware or software against a welldefined standard


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Not usually undertaken by small and medium

sized organisations

Requires a great deal of careful planning and

in-depth knowledge of the relevant standards

Testing - 6.21

Regression Testing

When a system is in its maintenance phase, and even earlierduring its development, a large number of changes may bemade to the program code in order to correct errors

a significant risk that these changes may re introduce previously


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a significant risk that these changes may re-introduce previously

corrected errors

Regression testing is designed to detect this type of error re-introduction

a series of tests that are run in succession and that are known to be

effective in finding the errors that have already been removed

usually automated regression test tools are widely used by maintenance programmers

Testing - 6.22

Test Teams

Testing must be a destructive process if it isto be successful

A successful test is one that discovers an


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A successful test is one that discovers anerror

Need a team of people independent of thedevelopment team, who have an incentive tofind errors

Costs are very high

Testing - 6.23

Designing and ImplementingTests

How do we design tests?

Desk checking and dry running code

Simple testing occurs when a program is compiledC t f h li f d


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Simple testing occurs when a program is compiledCount use of each l ine of code

Further errors can be detected at run-time by theOperating System or the interpreter, if using aninterpreted language

Difficult to test for logic

There is no substitute for human based testing

Testing - 6.24

Integrated Development

Environments (IDE)

These software tools make the process of editing,compiling linking running recording and


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These software tools make the process of edit ing,compiling, linking, running, recording anddebugging results more convenient

Used to handle all the files that make up a largeproject

Typically offer some programmer oriented features

Testing - 6.25

Design Guidelines for Effective

Tests

Need to look actively for conditions that are

likely to cause a system to fail


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likely to cause a system to fail

For black box testing scenarios we must lookat systems in terms of input, output and datastorage

Testing - 6.26

Further Reading on Testing

For those of you who wish to understand moreabout the whole process of testing, perhaps if you

intend to become a software engineer, we suggest


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g , ggyou read the chapter on

Software Testing in the text book:

Software Engineering, Ian Sommerville, Addison WesleyISBN 0 201 39815

Testing - 6.27

Design Guidelines - Inputs

Inputs:- screen layout - ease of use, clarity, handling of incorrect entries