Software engineering introduction

Introduction

Loganathan R

1Prof. R. Loganathan, CSE, HKBKCE

Loganathan R

Objectives• Understand what software engineering is

and its importance

• Know the answers to key questions aboutsoftware engineeringsoftware engineering

• Understand ethical and professional issuesthat are important for software engineers


Software costs• Software costs often dominate computer system

costs. The costs of software on a PC are oftengreater than the hardware cost.

• Software costs more to maintain than it does to• Software costs more to maintain than it does todevelop. For systems with a long life, maintenancecosts may be several times development costs.

• Software engineering is concerned with cost-effective software development.


Software engineering• Software engineering is concerned with

theories, methods and tools for professionalsoftware development.

• First proposed in 1968 at a conference held• First proposed in 1968 at a conference heldto discuss ‘Software Crisis’

• Informal software development is NOTenough for large & complex systems.

• Developed effective methods of S/WSpecification, Design & Implementation


FAQs about SE:

1.What is software?• Computer programs and associated documentation such as

requirements, design models and user manuals.

• Two fundamental types of software Products

• Generic Products• Developed to be sold to a range of different customers e.g. PC software such

as Excel or Word.as Excel or Word.

• Customised or Bespoke Products• developed for a single customer according to their specification.

• The difference is, for generic products the s/w specification iscontrolled by organisation(developed), for Customer products it isthe buying organisation.


FAQs about SE:

2.What is software engineering?• Software engineering is an engineering discipline

that is concerned with all aspects of softwareproduction.

• Software engineers should adopt a systematic and• Software engineers should adopt a systematic andorganised approach to their work and useappropriate tools and techniques depending onthe problem to be solved, the developmentconstraints and the resources available.


FAQs about SE:

3.What is the difference between softwareengineering and computer science?

• Computer Science is concerned with theory andfundamentals.

• Software Engineering is concerned with thepracticalities of developing and delivering usefulpracticalities of developing and delivering usefulsoftware.

• Computer Science theories are still insufficient(unlikePhysics & Electrical) to act as a completeunderpinning for software engineering (often use ofad hoc approaches).


FAQs about SE:

4. What is the difference between softwareengineering and system engineering?

• System engineering is concerned with all aspects ofcomputer-based systems development includinghardware, software and process engineering.

• Software engineering is part of this process• Software engineering is part of this processconcerned with developing the softwareinfrastructure, control, applications and databases inthe system.

• System engineers are involved in system specification,architectural design, integration and deployment.


FAQs about SE:

5.What is a software process?• A set of activities and associated results that produce

a software product.• Four common Fundamental process activities in all

software processes are:• Specification - what the system should do and its• Specification - what the system should do and its

development constraints.• Development - software system design and programming.• Validation - checking that the software is what the

customer wants.• Evolution - changing the software in response to changing

demands.


FAQs about SE:

6. What is a software process model?• A simplified representation of a software process, presented from a

specific perspective(one’s view).• Examples of process perspectives are

– Workflow Model (perspective )- Shows sequence of activities in the process withi/p, o/p and dependencies;

– Data-flow or Activity Model(perspective) – represents a set activities, whichcarries out some data transformation(shows how i/p to the process(spec) istransformed to o/p(design).transformed to o/p(design).

– Role/action model(perspective) – roles of the people & activities for which theare responsible(who does what).

• Generic process models– Waterfall – above activities are represented as separate process phase as

specification, design, implementation, testing and so on;– Iterative development – interleaves the activities of spec., development &

validation;– Component-based software engineering(CBSE)-focuses on integrating existing

parts .


FAQs about SE:

7. What are the costs of software engineering?

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

• Costs vary depending on the type of system being• Costs vary depending on the type of system beingdeveloped and the requirements of systemattributes such as performance and systemreliability.

• Distribution of costs depends on the developmentmodel that is used.


Activity cost distributionWat erfall model

It erative development

Specification Design Development Integ ration and testing

25 5 0 75 1000

2 5 5 0 75 1 000

Component-based software eng ineering

Development and evolution costs for long-lifetime syst ems

System evolution

10 200 30 4000

System development

Specification Development Integ ration and testing

2 5 5 0 75 1 000

Specification Iterative development System testing


Product development costs

25 50 75 1000


Specification Development System testing

FAQs about SE:

8.What are software engineering methods?• Structured approach to software development(Quality in a Cost

effective way) which include system models, notations, rules,design advice and process guidance.

• Methods Structured Analysis(Function Oriented)(1970) Object Oriented(1980s&1990s) UML(integrated into single approach) UML(integrated into single approach)

• Components used in these methods:• Model descriptions

• Descriptions of graphical models which should be produced;

• Rules• Constraints applied to system models;

• Recommendations• Advice on good design practice;

• Process guidance• What activities to follow.


FAQs about SE:

9. What is CASE?

• Computer-Aided Software Engineering.

• Software systems that are intended to provide automatedsupport for software process activities(requirementanalysis, system modelling ,testing & debugging).

• CASE systems are often used for method support.


FAQs about SE:

10. What are the attributes of good software?

• The software should deliver the required functionality andperformance to the user and should be maintainable, dependableand acceptable.

• Maintainability– Software must evolve to meet changing needs of customer;

• Dependability• Dependability– Software must be trustworthy(reliability, security & safety) ;

• Efficiency– Software should not make wasteful use of system resources(memory/CPU);

• Acceptability– Software must accepted by the users for which it was designed. This means it

must be understandable, usable and compatible with other systems.


FAQs about SE:

11.What are the key challenges facing software engineering?

• Heterogeneity, delivery and trust.

• Heterogeneity Challenge– Developing techniques for building software that can cope with

heterogeneous platforms and execution environments(Distributed systems);

• Delivery Challenge• Delivery Challenge– Developing techniques that lead to faster delivery of large and complex

systems without compromising quality;

• Trust Challenge– Developing techniques that demonstrate that software can be trusted by its

users.


Professional and ethical responsibility

• Software engineering involves widerresponsibilities than simply the application oftechnical skills.

• Software engineers must behave in an honest and• Software engineers must behave in an honest andethically responsible way if they are to berespected as professionals.

• Ethical behaviour is more than simply upholdingthe law.


Issues of professional responsibility

• Confidentiality– Engineers should normally respect the confidentiality

of their employers or clients irrespective of whether ornot a formal confidentiality agreement has beensigned.signed.

• Competence– Engineers should not misrepresent their level of

competence. They should not knowingly accept workwhich is outwith their competence.


Issues of professional responsibility

• Intellectual property rights

– Engineers should be aware of local laws governing the use ofintellectual property such as patents, copyright, etc. They shouldbe careful to ensure that the intellectual property of employersand clients is protected.and clients is protected.

• Computer misuse

– Software engineers should not use their technical skills tomisuse other people’s computers. Computer misuse ranges fromrelatively trivial (game playing) to extremely serious(dissemination of viruses).


ACM/IEEE Code of Ethics

• The professional societies in the US havecooperated to produce a code of ethical practice.

• Members of these organisations sign up to thecode of practice when they join.

• The Code contains EIGHT Principles related to the• The Code contains EIGHT Principles related to thebehaviour of and decisions made by professionalsoftware engineers, including practitioners,educators, managers, supervisors and policymakers, as well as trainees and students of theprofession.


Code of ethics - principles

• PUBLIC

– Software engineers shall act consistently with the publicinterest.

• CLIENT AND EMPLOYER

– Software engineers shall act in a manner that is in the bestinterests of their client and employer consistent with the publicinterest.

• PRODUCT

– Software engineers shall ensure that their products and relatedmodifications meet the highest professional standards possible.



• JUDGMENT

– Software engineers shall maintain integrity and independence intheir professional judgment.

• MANAGEMENT

Software engineering managers and leaders shall subscribe to– Software engineering managers and leaders shall subscribe toand promote an ethical approach to the management ofsoftware development and maintenance.

• PROFESSION

– Software engineers shall advance the integrity and reputation ofthe profession consistent with the public interest.



• COLLEAGUES

– Software engineers shall be fair to and supportive oftheir colleagues.

• SELF• SELF

– Software engineers shall participate in lifelong learningregarding the practice of their profession and shallpromote an ethical approach to the practice of theprofession.


Ethical dilemmas

• Disagreement in principle with the policies ofsenior management.

• Your employer acts in an unethical way andreleases a safety-critical system without finishingreleases a safety-critical system without finishingthe testing of the system.

• Participation in the development of militaryweapons systems or nuclear systems.


Software engineering introduction

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