01-The Scope of Software Engineering

7/29/2019 01-The Scope of Software Engineering

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Chapter 1:

The Scope of Software Engineering


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By the end of this module, you will...

Recall what a software is and identify its categories.

Understand what software engineering is. Understand why software engineering is important.

Know answers to key questions related to the software

engineering discipline.


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Quick Look

WHAT is it?: Computer software encompassesprograms that execute within a computer of any

size and architecture, documents that

encompass hard-copy and virtual forms, and

data that combine numbers and text but alsoincludes representations of pictorial, video, and

audio information.

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WHO does it?: Software engineers buildsoftware products by applying software

engineering approach.

WHY is it important?: Computer software areused in nearly every aspect of our lives.

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Software

Programs

DocumentationData

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Software: Where does it lie?

SystemDocumentation

UserDocumentation

It encompasses programs that execute

within a computer, documents that include

hard-copy & virtual forms, and data that

combine numbers and text but alsoincludes representations of pictorial, video,

and other information.


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The Evolving Role of Software

Software takes on a dual role:

It is a product

It is a vehicle for delivering a product

Significant change in its role has been

precipitated by:

Dramatic improvement in hardware performance

Profound change in computing architectures

Vast increases in memory and storage capacity

Wide variety of input and output options


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The Nature of Software

Software is intangible

Hard to understand development effort

Software is easy to reproduce but costly

In other engineering products, manufacturing is

the costly stage

In software, cost is in its development

Software is complex to develop esp. for

labor-intensive industry

Difficulty in automating some manual tasks


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The Nature of Software

Software quality problems are hard to notice

Finding all the errors in the software before

delivering it to the customer is difficult

Software is easy to modify

People make changes without fully understanding

the software

Software does not wear out

It deteriorates by having its design changed:

erroneously, or in ways that were not anticipated, thus

making it complex


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Types of Software

Custom / Bespoke

For a specific customer

Customization is based on user requirements

Generic

Sold on open market

Often called COTS (Commercial Off The Shelf)

Embedded

Intelligent products that reside in ROM

Built into hardware and is hard to modify/change


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Types of Software

Differences among custom, generic and

embedded software

Custom Generic EmbeddedNumber ofcopies in use low medium high

Total processing power

devoted to running this

type of software

low high medium

Worldwide annual

development effort

high medium low


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Specific Types of Software

Systems software

Programs written to service other programs

Include language translators, file management

utilities, operating systems, device drivers

Real time software

Programs that analyze and control real world

events

Include control and monitoring systems


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Business/Data processing software

Programs that facilitate business operations or

management decision making

Include payroll, sales & inventory, accounts

receivable/payable

Engineering & scientific software

Programs characterized by number crunchingalgorithms

Include applications used in the area of molecular

biology, volcanology, astronomy, systemsimulation, etc.


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Personal computer software

Commonly known as productivity tools

Include word processing, spreadsheets, computer

graphics, multimedia, entertainment, database

management, etc.

Web-base software

Web applications that incorporates executableinstructions (e.g. CGI, HTML, Perl, or Java)


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Artificial intelligence software

Programs that makes use of non-numerical

algorithms to solve complex problems that are not

amenable to computation or straightforwardanalysis

Include robotics, expert systems, knowledge-

based systems, pattern recognition (image and

voice), neural networks, theorem proving, game

playing


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Activity Think about all the devices and systems

that you encounter in your everyday lifewhich have software controlling them

List as many as you can

Virtually all countries

depend on complex

computer-based

systems.


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Why is Software Engineering important?

Complex systems need a disciplined approach for

designing, developing and managing them.


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Software Development Crises

Projects were:

Late Over budget

Unreliable

Difficult to maintain

Performed poorly

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Software errors incur cost.

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The Cost of Software Engineering

The cost depends on:

The type of software being developed, and The process used in software development

Each generic approach has a different profile of cost distribution.

Roughly 60% of costs are development costs, 40% are testing

costs.

For custom software, cost distribution depends on the process

used.

Evolution costs often exceed development costs.

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Cost distribution

Generic software development (COTS)

Product development costs

0 25 50 75 100

Specification Development System testing

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Cost distribution

Custom software development (Bespoke)Software Model

Cost units

Cost distribution

Software development activity

Waterfall Model

0 25 50 75 100

Specification Design Development Integration and testing

Iterative Development

0 25 50 75 100

Specification Iterative Development System testing

Component-based Software Engineering

0 25 50 75 100

Specification Development Integration and testing

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Errors in computer software can havedevastating effects.

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Software Crisis

Example 2: Ariane 5 Explosion

European Space Agency spent 10 years and $7

billion to produce Ariane 5.

Crash after 36.7 seconds.

Caused by an overflow error. Trying to store a 64-bit

number into a 16-bit space.

Watch the video:

http://www.youtube.com/watch?v=z-r9cYp3tTE

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Software Crisis

Example 1: 2009,Computer glitch delays flights

Dozens of flights from the UK were delayed Saturday after

a glitch in an air traffic control system in Scotland, but theproblem was fixed a few hours later.

The agency said it reverted to backup equipment as

engineering worked on the system.

The problem did not create a safety issue but could cause

delays in flights.

Read more at:

http://edition.cnn.com/2009/WORLD/europe/10/03/uk.fl

ights.delayed

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Software Crisis

Example 3: 1992, London Ambulance Service

Considered the largest ambulance service in the

world.

Caused by database overload problem.

It was unable to keep track of the ambulances

and their statuses. Sending multiple units to some

locations and no units to other locations.

Generates many exceptions messages.

46 deaths.

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Therefore

A well-disciplined approach to

software development and

management is necessary. This is

called software engineering.

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Software Engineering: Historical Aspects

The term software engineering first appeared in the 1968 NATO

Software Engineering Conference and was meant to provokethought regarding what was then called the softwarecrisis..

.. An engineering discipline that is concerned with all aspects of

software production from the early stages of system specificationto maintaining the system after it has gone into use. Sommerville,

pg.7


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Software Engineering and the

Engineering Profession The term Software Engineering was coined in 1968

People began to realize that the principles of engineeringshould be applied to software development

Engineering is a licensed profession In order to protect the public

Engineers design artifacts following well acceptedpractices which involve the application of science,

mathematics and economics Ethical practice is also a key tenet of the profession

In many countries, much software engineering does not

require an engineering license, but is still engineering

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Software Engineering vs. Computer Science

Computer science is no more about computers than

astronomy is about telescopes. Edsger Dijkstra

Computer Science

Theory.

Fundamentals.

Software Engineering

Practicalities of softwaredesign, development anddelivery.

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Software Engineering vs. Systems Engineering

Systems Engineering:

Interdisciplinary engineering field (computer, software, and process eng.).

Focuses on how complex engineering projects should be designed and managed.

Systems Engineering

All aspects of computer-based systemsdevelopment: HW + SW +Process.

Older than SWE.

Software Engineering

Deals with the design,development and deliveryof SW.

Is part of SystemsEngineering.


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The process of solving customers problems by

the systematic development and evolution of

large, high-quality software systems within

cost, time and other constraints.

Other definitions: IEEE: (1) the application of a systematic, disciplined, quantifiable approach to

the development, operation, maintenance of software; that is, the applicationof engineering to software. (2) The study of approaches as in (1).

The Canadian Standards Association: The systematic activities involved in the

design, implementation and testing of software to optimize its production and

support.

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What is Software Engineering?

To solve customers problems

To utilize systematic development

To produce high-quality softwareTo produce software within the

allotted budget & time


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Goals of Software Engineering

Solving customers problems

This is the goalof software engineering

Sometimes the solution is to buy, not build

Adding unnecessary features does not help solve

the problem

Software engineers must communicate effectively

with the customers to identify and understand theproblem


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Systematic development and evolution

An engineering process involves applying well

understood techniques in a organized and

disciplinedway Many well-accepted practices have been formally

standardized

e.g. by the IEEE or ISO

Most development work is evolutionary


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Large, high quality software systems

Software engineering techniques are needed

because large systems cannot be completely

understoodby one person Teamwork and co-ordination are required

Key challenge: Dividing up the work and ensuring

that the parts of the system work properlytogether

The end-product must be of sufficient quality


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Cost, time and other constraints

Finite resources

The benefit must outweigh the cost

Others are competing to do the job cheaper and

faster

Inaccurate estimates of cost and time have caused

many project failures


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1. Users

Those who use the software

2. Customers

Those who pay for the software

3. Software developers

Include system analysts, system designers, system

builders

4. Development Managers

All four roles can be fulfilled by the same person37

Stakeholders in Software Engineering


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Software Quality and the Stakeholders

QUALITY

SOFTWARE

Developer:easy to design;

easy to maintain;easy to reuse its parts

User:

easy to learn;

efficient to use;

helps get work done

Customer:solves problems at

an acceptable cost in

terms of money paid and

resources used

Development manager:sells more and

pleases customers

while costing lessto develop and maintain

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Functional Attributes of a Software

Functional attributes

System performance; what the system does;

capability of the software to provide functions which

meet stated and implied needs when the software is

used

Key Goal: To capture the required behavior of asoftware system in terms of functionality and the

technology implementation through a system analysis

process.

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Non-Functional Attributes of a Software

Non-functional attributes

System quality; how the system does it; based on the

parameters of system performance, software quality

attributes, reliability and security, cost, constraints in

design and implementation

Key goal: To determine the factors that can be used tojudge the operation of a system or the quality attributes

of the system.

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Some Attributes of a Good Software

Product Characteristic Description

Usability Easy to learn how to use the system by target users.Efficient to use the system by users to accomplish a

task.

Satisfying to use by intended users.

Maintainability Evolution qualities such as testability, extensibility.

Dependability Reliability, security, safety.

Efficiency Response time, processing time, memory utilization.

Reusability Reprogramming is not needed.

http://en.wikipedia.org/wiki/Non-functional _requirement

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http://en.wikiepedia.org/wiki/Non-functionalhttp://en.wikiepedia.org/wiki/Non-functional


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Activity

What are the key attributes for..

Interactive game Banking systemCardiac monitor in an ICU

unit

Players, score, scenes,

theme.

Client accounts, stocks

bonds, money transfers.

heart rate, temperature,

blood pressure.


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Software Quality: Conflicts & Objectives

The different qualities can conflict Increasing usability can reduce efficiency

Increasing efficiency can reduce maintainability orreusability

Setting objectives for quality is a key engineeringactivity

You then design to meet the objectives

Avoids over-engineering which wastes money

Optimizing is also sometimes necessary E.g. obtain the highest possible reliability using a fixed

budget

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Challenges Facing Software Engineering

Challenge Why? Software needs to ..

HeterogeneityDifferent computers, different

platforms, different support systems.Cope with this variability.

Delivery

Businesses are more responsive

supporting software needs toevolve rapidly.

Be delivered in shorter timewithout compromising quality.

TrustSoftware is a part of many aspects of

our lives (work, study, leisure).Demonstrate that it can be

trusted by users.


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Software Engineering Projects

1. Most projects are evolutionaryor

maintenance projects, involving work on

legacysystems

Development and evolution costs for long-lifetime systems

0 100 200 300 400

System development System evolution


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Corrective projects: fixing defects

Adaptive projects: changing the system in

response to changes in

Operating system, Database, Rules and regulations Enhancement projects: adding new features for

users

Reengineering or perfective projects: changing

the system internally so it is more maintainable


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2. Greenfield projects

New development; project that lacks anyconstraints imposed by prior work; theres noneed to remodel or demolish an existing structure

Minority of projects are greenfield; projects thatare often coveted by engineers

Examples: Cellular networks, power plant, airports


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3. Projects that involve building on aframeworkor a set of existing components.

A framework is an application that is missing some

important details. E.g. Specific rules of this organization.

Such projects: Involve plugging together components that are:

Already developed. Provide significant functionality.

Benefit from reusing reliable software.

Provide much of the same freedom to innovate foundin green field development.


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Information Systems Framework

This provides a unifying framework, inspiredby the works ofJohn Zachman, by whichvarious people with different perspectives can

organize and view the fundamental buildingblocks ofsoftware projects.

1. DATA

2. PROCESSES

3. INTERFACES


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Activities Common to Software Projects

Requirements and specification

Includes

Domain analysis

Defining the problem Requirements gathering

Obtaining input from as many sources as possible

Requirements analysis

Organizing the information

Requirements specification

Writing detailed instructions about how the software should

behave


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Design Deciding how the requirements should be

implemented, using the available technology

Includes: Systems engineering: Deciding what should be in

hardware and software

Software architecture: Dividing the system intosubsystems and deciding how the subsystems willinteract

Detailed design of the internals of a subsystem

User interface design

Design of databases


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Modeling Creating representations of the domain or the software

Use case modeling

Structural modeling

Dynamic and behavioural modeling

Programming

Quality assurance Reviews and inspections

Testing

Deployment

Managing the process

Diffi lti d Ri k i S ft


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Difficulties and Risks in Software

Engineering

Complexity and large numbers of details

Uncertainty about technology

Uncertainty about requirements

Uncertainty about software engineering skills

Constant change

Deterioration of software design Political risks (considered as wicked problem)


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Software Depression

The software crisis has not been solved:

- Data on 9236 projects completed in 2004


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Cutter Consortium Data

2002 survey of information technology

78% have been involved in disputes ending in litigation

For the organizations that entered into litigation:

In 67% of the disputes, the functionality of the informationsystem as delivered did not meet up to the claims of the

developers

In 56% of the disputes, the promised delivery date slipped

several times In 45% of the disputes, the defects were so severe that the

information system was unusable


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Software Myths: Practitioners View

Once we write the program and get it to work, our

job is done.

Until I get the program running I have no way of

assessing its quality. The only deliverable work product for a successful

project is the working program.

Software engineering will make us create voluminous

and unnecessary documentation and will invariably

slow us down.

Documents

01-The Scope of Software Engineering