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Software Engineering

Ian Sommerville- 2004 7th edition

Instructor: Mrs. Eman ElAjrami

University Of Palestine

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Chapter 1 Introduction

What is Software Engineering?

Why we need Software Engineering?

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Software engineering

The economies of ALL developed nations are dependent on software (ideas and technological discoveries are the driving engines of the economic growth)

More and more systems are software controlled

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Software costs

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

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FAQs about software engineeringWhat is software?What is software engineering?What is the difference between software engineering

and computer science?What is the difference between software engineering

and system engineering?What is a software process?What is a software process model?What are the costs of software engineering?What are software engineering methods?What is CASE (Computer-Aided Software

Engineering)What are the attributes of good software?What are the key challenges facing software

engineering?

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What is Software?Software is a set of items or objects that form a

“configuration” that includes: • programs • documents • data ...Software is a productSoftware is a vehicle for delivering a productsoftware is engineered, it is not manufacturedsoftware doesn’t wear out, Not like hardware which exhibits

relatively high failure rate early in its life, then defects are corrected and failure rate drops to a steady level then later on the failure rates rise again as the hardware components suffer from the cumulative affect of dust, vibration …etc. The software on the other hand, the failure rate is due to side effects to changes and modifications.

software is complex

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What is Software?

Computer programs and associated documentation

Software products may be developed for a particular customer or may be developed for a general market

Software products may beGeneric - developed to be sold to a range of different customers

Bespoke (custom) - developed for a single customer according to their specification

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What is Software? (cont.)System software, compilers, editors.

-Real time software, software that monitor/control real world event.

-Embedded software read only memory, keypad of microwave oven

-Personal computer software.

-Web based software.

Advice: Work very hard to understand what you have to do before you start.

You may not be able to develop every detail, but the more you know, the less risk you take

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What is software engineering?

Software engineering is an engineering discipline which is concerned with all aspects of software production

Software engineers should adopt: a systematic and organized approach to their

work use appropriate tools and techniques depending

on the problem to be solved

Engineers make thing work, they apply theories, methods and tools where these are appropriate.

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What is software engineering? (cont.)Software engineering is: the systematic use of

many disciplines, tools, and resources for the practical application.

This is a broad definition which includes everything except hardware.

Engineering is the art and science of managing engines for practical application.

To manage these engines, we have to consider all aspects of the intended applications, such as operational concepts, requirements, design, development, and maintenance.

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What is the difference between software engineering and computer science?

Computer science is concerned with theory and fundamentals; software engineering is concerned with the practicalities of developing and delivering useful software

Computer science theories are currently insufficient to act as a complete foundation or basis for software engineering

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What is the difference between software engineering and system engineering?

System engineering is concerned with all aspects of computer-based systems development including hardware, software and process engineering. Software engineering is part of this process

System engineers are involved in system specification, architectural design, integration of the finish system.

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What is a software process?

A set of activities whose goal is the developmentor evolution of software

Generic activities in all software processes are:Specification - what the system should do

and its development constraintsDevelopment - production of the software

systemValidation - checking that the software is

what the customer wantsEvolution - changing the software in

response to changing demands

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What is a software process model?• A simplified representation of a software process,

presented from a specific perspective (type) • OR• An abstraction of the actual process which is being• described.

• Generic process models:

o Waterfall, each activity in a separate process, you start next one after signing off the previous.

o Evolutionary development (iterative), rapidly develop the initial system, then refine each of these activities until you reach a complete system

o Integration from reusable components, integration of new components (bought or developed) with an existing system

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What are the costs of software engineering?

Roughly 60% of costs are development costs, 40% are testing costs. For custom software, evolution costs often exceed development costs

Costs vary depending on the type of system being developed and the requirements of system attributes such as performance and system reliability

Distribution of costs depends on the development model that is used (see next slide).

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Waterfall model

Iterative development

Component-based software engineering

Development and evolution costs for long-lifetime systems

System evolution

10 200 30 4000

System development

Specification Design Development Integration and testing

25 50 75 1000

Specification Development Integration and testing

25 50 75 1000

Specification Iterative development System testing

25 50 75 1000

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What is CASE (Computer-Aided Software Engineering)

Software systems which are intended to provide automated support for software process activities.

CASE systems are often used for method support

Upper-CASETools to support the early process activities of requirements and design

Lower-CASETools to support later activities such as programming, debugging and testing

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What are the attributes of good software?

The software should deliver the required functionality and performance to the user and should be maintainable, dependable, efficient and usable

MaintainabilitySoftware must evolve to meet changing needs

Dependability Dependability includes (reliability, security

and safety) , dependable software should not cause damage in the event of failure.

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What are the attributes of good software?

EfficiencySoftware should NOT make wasteful use of

system resources such as memory and processor time.

UsabilitySoftware must be usable by the users for

which it was designed, it should have an appropriate user interface and enough documentation.

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What are the key challenges facing software engineering?

Coping with legacy systems ( old, valuable systems must be maintained and updated), coping with increasing diversity and coping with demands for reduced delivery times.

Heterogeneity, systems are required to operate as distributed across networks that include a different type of hardware and software

Delivery, there is increasing pressure for faster delivery of software

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Issues of professional responsibilityConfidentiality الخصوصيه

Engineers should normally respect the confidentiality of their employers or clients.

Competence الكفاءة Engineers should not misrepresent their level of

competence. They should not accept work which is out with their competence.

Intellectual property rights Engineers should be aware of local laws governing the

use of intellectual property such as patents, copyright, etc. They should be careful to ensure that the intellectual property of employers and clients is protected.

Computer misuse Software engineers should not use their technical skills

to misuse other people’s computers. Computer misuse ranges from relatively trivial (game playing on an employer’s machine) to extremely serious (viruses).

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Key pointsSoftware engineering is an engineering

discipline which is concerned with all aspects of software production.

Software products consist of developed programs and associated documentation.

Essential product attributes are maintainability, dependability, efficiency and usability.

The software process consists of activities which are involved in developing software products.

Basic activities are software specification, development, validation and evolution.

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Key pointsCASE tools are software systems which are

designed to support activities in the software process such as editing design diagrams, checking diagram consistency and keeping track of program tests which have been run.

Software engineers have responsibilities to the engineering profession and society. They should not simply be concerned with technical issues.