Software engineering introduction

Introduction
Loganathan R

Prof. R. Loganathan, CSE, HKBKCE 1

Objectives
• Understand what software engineering is
and its importance
• Know the answers to key questions about
software engineering
• Understand ethical and professional issues
that are important for software engineers


Software costs
• Software costs often dominate computer 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 engineering
• Software engineering is concerned with
theories, methods and tools for professional
software development.
• First proposed in 1968 at a conference held
to discuss ‘Software Crisis’
• Informal software development is NOT
enough for large & complex systems.
• Developed effective methods of S/W
Specification, 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.
• Customised or Bespoke Products
• developed for a single customer according to their specification.
• The difference is, for generic products the s/w specification is
controlled by organisation(developed), for Customer products it is
the buying organisation.


FAQs about SE:
2.What is software engineering?
• Software engineering is an engineering discipline
that is concerned with all aspects of software
production.
• Software engineers should adopt a systematic and
organised approach to their work and use
appropriate tools and techniques depending on
the problem to be solved, the development
constraints and the resources available.


FAQs about SE:
3.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 still insufficient(unlike
Physics & Electrical) to act as a complete
underpinning for software engineering (often use of
ad hoc approaches).


FAQs about SE:
4. 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
concerned with developing the software
infrastructure, control, applications and databases in
the 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
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 with
i/p, o/p and dependencies;
– Data-flow or Activity Model(perspective) – represents a set activities, which
carries out some data transformation(shows how i/p to the process(spec) is
transformed to o/p(design).
– Role/action model(perspective) – roles of the people & activities for which the
are 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, 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.


Activity cost distribution
Wat erfall model
0 25 50 75 100

Specification Design Development Integ ration and testing

It erative development

0 25 50 75 1 00

Specification Iterative development System testing

Component-based software eng ineering

0 25 50 75 1 00

Specification Development Integ ration and testing

Development and evolution costs for long-lifetime syst ems
0 10 200 30 400

System development System evolution


Product development costs

0 25 50 75 100

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)
• 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 automated
support for software process activities(requirement
analysis, 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 and
performance to the user and should be maintainable, dependable
and acceptable.
• Maintainability
– Software must evolve to meet changing needs of customer;
• 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
– 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 wider
responsibilities than simply the application of
technical skills.
• Software engineers must behave in an honest and
ethically responsible way if they are to be
respected as professionals.
• Ethical behaviour is more than simply upholding
the law.


Issues of professional responsibility
• Confidentiality
– Engineers should normally respect the confidentiality
of their employers or clients irrespective of whether or
not a formal confidentiality agreement has been
signed.
• Competence
– Engineers should not misrepresent their level of
competence. They should not knowingly accept work
which is outwith their competence.


Issues of professional responsibility
• 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) to extremely serious
(dissemination of viruses).


ACM/IEEE Code of Ethics
• The professional societies in the US have
cooperated to produce a code of ethical practice.
• Members of these organisations sign up to the
code of practice when they join.
• The Code contains EIGHT Principles related to the
behaviour of and decisions made by professional
software engineers, including practitioners,
educators, managers, supervisors and policy
makers, as well as trainees and students of the
profession.


Code of ethics - principles
• PUBLIC
– Software engineers shall act consistently with the public
interest.
• CLIENT AND EMPLOYER
– Software engineers shall act in a manner that is in the best
interests of their client and employer consistent with the public
interest.
• PRODUCT
– Software engineers shall ensure that their products and related
modifications meet the highest professional standards possible.


• JUDGMENT
– Software engineers shall maintain integrity and independence in
their professional judgment.
• MANAGEMENT
– Software engineering managers and leaders shall subscribe to
and promote an ethical approach to the management of
software development and maintenance.
• PROFESSION
– Software engineers shall advance the integrity and reputation of
the profession consistent with the public interest.


• COLLEAGUES
– Software engineers shall be fair to and supportive of
their colleagues.
• SELF
– Software engineers shall participate in lifelong learning
regarding the practice of their profession and shall
promote an ethical approach to the practice of the
profession.


Ethical dilemmas
• Disagreement in principle with the policies of
senior management.
• Your employer acts in an unethical way and
releases a safety-critical system without finishing
the testing of the system.
• Participation in the development of military
weapons systems or nuclear systems.


Software engineering introduction

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