lesson 1 software engineering

8/3/2019 Lesson 1 Software Engineering

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Intro to Software Engineering

Software Engineering

Lesson 1


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Software Engineering

The establishment and use of sound engineering

principles in order to obtain economically,

software that is reliable and works efficiently onreal machines


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Introduction to Software Engineering

Objectives

Define Software

Identify software components, evolution &

application

Define Software Engineering

Discuss software paradigms


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What is Software ?

A set of instructions which when executed

provide desired functions & performance

Data structures that enable programs to

adequately manipulate data & information


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Software DefinitionDefinitions ofSoftware on the Web:

A computer program, which provides the instructions whichenable the computer hardware to work. System software,such as Windows or MacOS, operate the machine itself,

and applications software, such as spreadsheet or wordprocessing programs, provide specific functionality.www.getnetwise.org/glossary.php

Computer programs; instructions that make hardware work.Two main types of software are system software

(operating systems), which control the workings of thecomputer, and applications, such as word processingprograms, spreadsheets, and databases.www.microsoft.com/office/newtosite/glossary.asp
http://www.getnetwise.org/glossary.phphttp://www.microsoft.com/office/newtosite/glossary.asphttp://www.microsoft.com/office/newtosite/glossary.asphttp://www.getnetwise.org/glossary.php


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Characteristics of Software It is developed or engineered, not manufactured in the classical

sense

Most software is custom-built, rather than being built fromcomponents

It does not wear out

Software is intangible Hard to understand development effort

Software is easy to reproduce Cost is in its development

in other engineering products, manufacturing is the costly stage

The industry is labor-intensive Hard to automate


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The Nature of Software ...

Untrained people can hack something

together

Quality problems are hard to notice

Software is easy to modify

People make changes without fully

understanding it

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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The Nature of Software

Conclusions

Much software has poor design and is getting

worse

Demand for software is high and rising

We are in a perpetual software crisis

We have to learn to engineer software


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Types of Software...

Custom

For a specific customer

GenericSold on open market

Often called

COTS (Commercial Off The Shelf)

Shrink-wrapped

Embedded

Built into hardware

Hard to 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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Types of Software

Real time software

E.g. control and monitoring systems

Must react immediately

Safety often a concern

Data processing software

Used to run businesses

Accuracy and security of data are key

Some software has both aspects


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What is Software Engineering?...

The process of solving customers problemsby the systematic development and

evolution of large, high-quality softwaresystems within cost, time and otherconstraints


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What is SE?

Solving customers problems

This is the goal of software engineering

Sometimes the solution is to buy, not build

Adding unnecessary features does not help

solve the problem

Software engineers must communicateeffectively to identify and understand the

problem


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What is Software Engineering?

Systematic development and evolution

An engineering process involves applying wellunderstood techniques in a organized and disciplined

way

Many well-accepted practices have been formallystandardized

e.g. by the IEEE or ISO

Most development work is evolution


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What is SE?

Large, high quality software systems

Software engineering techniques are needed because

large systems cannot be completely understood by oneperson

Teamwork and co-ordination are required

Key challenge: Dividing up the work and ensuring that

the parts of the system work properly together The end-product that is produced must be of sufficient

quality


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What is Software Engineering?

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 havecaused many project failures


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Software costs often dominate system costs. The

costs of software on a PC are often greater than

the hardware cost Software costs more to maintain than it does to

develop. For systems with a long life,

maintenance costs may be several times

development costs

Software engineering is concerned with cost-

effective software development

Software costs


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Stakeholders in Software

Engineering1. Users

Those who use the software

2. Customers

Those who pay for the software

3. Software developers

4. Development Managers

All four roles can be fulfilled by the same person


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Software Quality...

Usability

Users can learn it and fast and get their job done easily

Efficiency

It doesnt waste resources such as CPU time and memory Reliability

It does what it is required to do without failing

Maintainability

It can be easily changed Reusability

Its parts can be used in other projects, so reprogramming is not

needed


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Software Quality...

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 atan acceptable cost in

terms of money paid and

resources used

Development manager:

sells more and

pleases customerswhile costing less

to develop and maintain


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Software Quality

The different qualities can conflict

Increasing efficiency can reduce maintainability orreusability

Increasing usability can reduce efficiency

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 fixedbudget


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Importance of product characteristics

The relative importance of these characteristics

depends on the product and the environment in

which it is to be used In some cases, some attributes may dominate

In safety-critical real-time systems, key attributes

may be dependability and efficiency

Costs tend to rise exponentially if very highlevels of any one attribute are required


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Efficiency costsCost

Efficiency


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Questions

Why so long to complete programs ?

Why costs so high ?

Why still contain errors when handed over ?

Why so difficult to measure progress ?


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The END

Zainudin Johari

Senior Lecturer

Unity

B Sc. (Hons) Computer Science, UPM

M Sc. Computer Science (Information Systems) UPM

lesson 1 software engineering

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