SE 262

Lecture 1

Introduction
To
Software Engineering

Spring 2024
1
Are you looking for this key?

Source: adapted from Ian Sommerville's lecture notes: SE9 6 2

Paying attention Hard work

Source: adapted from Ian Sommerville's lecture notes: SE9 3

How to do well in this course?
➢ BEFORE EVERY LECTURE
➢ Read the relevant portion of the textbook

➢ DURING EVERY LECTURE

➢ Take notes!
➢ Ask questions if anything is not clear

➢ AFTER EVERY LECTURE

➢ Review the lecture slides.
➢ IF anything is not clear THEN
➢ (discuss it with your fellow students) AND
➢ (ask me about it at the beginning of the next lecture)

Source: adapted from Ian Sommerville's lecture notes: SE9 4

Introduction

Source: adapted from Ian Sommerville's lecture notes: SE9 5

Software Products
❑ Generic products
❑ Stand-alone systems that are marketed and sold to any customer who wishes to buy them. Examples:
graphics programs, project management tools, CAD software, ….etc.

❑ The specification of what the software should do is owned by the software developer and decisions
on software change are made by the developer.

❑ Customized products
❑ Software that is commissioned by a specific customer to meet their own needs. Examples :
embedded control systems, air traffic control software,….etc.

❑ The specification of what the software should do is owned by the customer and they make decisions
on software changes that are required.

Source: adapted from Ian Sommerville's lecture notes: SE9 6

Software Costs
❑ Software costs often dominate computer system costs.

❑ Software costs more to maintain than it does to develop.

❑ For systems with a long life, maintenance costs may be several

times development costs.

Source: adapted from Ian Sommerville's lecture notes: SE9 7

Importance of S/W Engineering
❑ More and more, individuals and society rely on advanced software
systems. We need to be able to produce reliable and trustworthy
systems economically and quickly.

❑ It is usually cheaper, in the long run, to use software engineering

methods and techniques for software systems.

❑ For most types of system, the majority of costs are the costs of
changing the software after it has gone into use.

Source: adapted from Ian Sommerville's lecture notes: SE9 8

Software Engineering
is an engineering discipline that is…..

❑ Concerned with theories, methods and tools for professional and cost-
effective software development.

❑ Concerned with all aspects of software production from the early stages of
system specification through to maintaining the system after it has gone into
use. i.e. Not just technical process of development. Also project management
and the development of tools, methods etc. to support software production.

Source: adapted from Ian Sommerville's lecture notes: SE9 9

Frequently asked questions about software engineering
Question Answer

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.

What are the attributes of good Good software should deliver the required functionality and
software? performance to the user and should be maintainable,
dependable and usable.

What is software engineering? Software engineering is an engineering discipline that is

concerned with all aspects of software production.

What are the fundamental software Software specification, software development, software
engineering activities? validation and software evolution.

What is the difference between Computer science focuses on theory and fundamentals;
software engineering and software engineering is concerned with the practicalities of
computer science? developing and delivering useful software.

What is the difference between System engineering is concerned with all aspects of
software engineering and system computer-based systems development including hardware,
engineering? software and process engineering. Software engineering is
part of this more general process.

Source: adapted from Ian Sommerville's lecture notes: SE9 10

Essential Attributes of Good Software
Product characteristic Description

Maintainability Software should be written in such a way so that it can evolve to meet
the changing needs of customers. This is a critical attribute because
software change is an inevitable requirement of a changing business
environment.

Dependability and Software dependability includes a range of characteristics including

security reliability, security and safety. Dependable software should not cause
physical or economic damage in the event of system failure. Malicious
users should not be able to access or damage the system.

Efficiency Software should not make wasteful use of system resources such as
memory and processor cycles. Efficiency therefore includes
responsiveness, processing time, memory utilisation, etc.

Acceptability Software must be acceptable to the type of users for which it is designed.
This means that it must be understandable, usable and compatible with
other systems that they use.

Source: adapted from Ian Sommerville's lecture notes: SE9 11

Software Process Activities
S/W specification, where customers and engineers define the
software that is to be produced and the constraints on its operation.

S/W development, where the software is designed and programmed.

S/W validation, where the software is checked to ensure that it is what

the customer requires.

S/W evolution, where the software is modified to reflect changing

customer and market requirements.

Source: adapted from Ian Sommerville's lecture notes: SE9 12

Software Engineering Diversity
There are many different types of software systems and there is no universal set of
software techniques that is applicable to all of these. As such, the software
engineering methods and tools used depend on:

1) the type of application being developed,

2) the requirements of the customer, and
3) the background of the development team.

However, some fundamental principles apply to all types of software systems,

irrespective of the development techniques used. See next slide!

Source: adapted from Ian Sommerville's lecture notes: SE9 13

S/W Engineering Fundamentals
Some fundamental principles apply to all types of software systems, irrespective of the
development techniques used:

1. Systems should be developed using a managed and understood development process.

Of course, different processes are used for different types of software.

2. Dependability and performance are important for all types of system.

3. Understanding and managing the software specification and requirements (what the
software should do) are important.

4. Where appropriate, you should reuse software that has already been developed rather
than write new software.

Source: adapted from Ian Sommerville's lecture notes: SE9 14

Application Types
Another classification..
❑ Stand-alone applications.
Run on a local computer and include all necessary
functionality. They do not need to be connected to a network.

❑ Interactive transaction-based applications

Execute on a remote computer and are accessed by users
from their own PCs or terminals (e. g. Web applications, such as E-commerce
applications.

❑ Embedded control systems

S/W systems that control and manage hardware devices.

❑ Data collection systems

Systems that collect data from their environment using a
set of sensors and send that data to other systems for processing.
Source: adapted from Ian Sommerville's lecture notes: SE9 15
Application Types – Cont.
❑ Batch processing systems
These are business systems that are designed to process
data in large batches. They process large numbers of individual inputs to
create corresponding outputs.

❑ Entertainment systems
Primarily for personal use and are intended to entertain the user.

❑ Systems for modeling and simulation

Developed by scientists and engineers to model physical
processes or situations, which include many, separate, interacting objects.

❑ Systems of systems
These are systems that are composed of a number of other software
systems.
Source: adapted from Ian Sommerville's lecture notes: SE9 16
Software Engineering &The Web
❑ The Web is now a platform for running applications, and organizations are
increasingly developing web-based systems rather than local systems.

❑ Web services* allow application functionality to be accessed over the

web.

❑ Cloud computing is an approach to the provision of computer services where

applications run remotely on the ‘cloud’. Users do not buy software, but
rather pay according to their use.

* For more information about Web Services see Chapter 19 in the textbook

Source: adapted from Ian Sommerville's lecture notes: SE9 17

Web-Based S/W Engineering
❑ Software reuse is the dominant approach for constructing web-based
systems.
When building these systems, you think about how you can assemble them from pre-existing
software components and systems.

❑ Web-based systems should be developed and delivered incrementally.

Web-based systems are usually, complex distributed systems and it is now generally recognized
that it is impractical to specify all the requirements for such systems in advance.

❑ User interfaces are constrained by the capabilities of web browsers.

Technologies such as AJAX allow rich interfaces to be created within a web browser but are still
difficult to use. Web forms with local scripting are more commonly used.

Source: adapted from Ian Sommerville's lecture notes: SE9 18

General Issues Affecting Most Software
❑ Heterogeneity
Increasingly, systems are required to operate as distributed systems across networks that include
different types of computer and mobile devices.

❑ Business and social change

Business and society are changing incredibly quickly as emerging economies develop and new
technologies become available. They need to be able to change their existing software and to
rapidly develop new software.

❑ Security and trust

As software is intertwined with all aspects of our lives, it is essential that we can trust that
software.

Source: adapted from Ian Sommerville's lecture notes: SE9 19

Software engineering ethics
❑ 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 but

involves following a set of principles that are morally correct.

Source: adapted from Ian Sommerville's lecture notes: SE9 20

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 out with their
competence.

Source: adapted from Ian Sommerville's lecture notes: SE9 21

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 on an
employer’s machine, say) to extremely serious (dissemination of viruses).

Source: adapted from Ian Sommerville's lecture notes: SE9 22

So far….
We continued with the introduction to software engineering and professional
software development. Particularly:
▪ Attributes of good software
▪ Software process activities
▪ Software engineering fundamentals
▪ Software engineering diversity and application types
▪ Software engineering and the Web
▪ General issues that affect most software
▪ Software engineering ethics

Source: adapted from Ian Sommerville's lecture notes: SE9 23

Key Points…
❑The Software engineering is an engineering discipline that is
concerned with all aspects of software production.
❑Essential software product attributes are maintainability,
dependability and security, and acceptability.
❑The fundamental principles and ideas of software engineering
are universally applicable to all types of system development.

❑There are many different types of system, and each requires

appropriate software engineering tools and techniques for their
development.

Source: adapted from Ian Sommerville's lecture notes: SE9 24

Next lecture...

We well have a look at the

“Software Processes”.

Source: adapted from Ian Sommerville's lecture notes: SE9 25