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Introduction W01



Software Engineering

  • This module builds on what you have learnt in:
    Year 3 Object Oriented Anyalysis and Design
  • 1 Lectures 2 Practical
  • Final Exam: 60%
  • Continuous Assessment: 40%
  • 2 assignments
  • Course text : Software Engineering. 9th Ed. 2011. Sommerville.
  • Notes and other materials are available at: http://lyitbb.blackboard.com

Learning Outcomes

  • Compare and contrast software process models and select a suitable software process model for use on a software project.
  • Evaluate quality in the software process and process improvement initiatives.
  • Appraise software quality models.
  • Establish a software measurement programme.
  • Manage software configuration for a software project.

Software Process

  • The activities of software process.
  • Software process models.
  • Coping with change

Agile Software Development

  • The agile manifesto.
  • Agile methods.
  • Agile development techniques.

Software Quality

  • Software quality models.
  • Quality management.
  • Process improvement.

Software measurement and metrics

  • The importance of measurement.
  • Internal Product attributes.
  • External Product attributes.
  • Planning a measurement program GQM.

Configuration Management

  • Version management.
  • System building.
  • Change management.
  • Release management.

What is Software Engineering

Sommerville Software Engineering 10th edition

  • What is software?
  • What is software engineering?
  • What is a software process?

Software Engineering

  • The economies of ALL developed nations are dependent on software.
  • More and more systems are software controlled.
  • Software engineering is concerned with theories, methods and tools for professional software development.
  • Expenditure on software represents a significant fraction of GNP in all developed countries.

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
  • Software engineering is concerned with cost-effective software development

Software Project Failure

  • Increasing system complexity
    • As new software engineering techniques help us to build larger, more complex systems, the demands change. Systems have to be built and delivered more quickly; larger, even more complex systems are required; systems have to have new capabilities that were previously thought to be impossible.
  • Failure to use software engineering methods
    • It is fairly easy to write computer programs without using software engineering methods and techniques. Many companies have drifted into software development as their products and services have evolved. They do not use software engineering methods in their everyday work. Consequently, their software is often more expensive and less reliable than it should be.

Frequently Asked Questions about software engineering

  • 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 software?
    Good software should deliver the required functionality and 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 engineering activities?
    Software specification, software development, software validation and software evolution.
  • What is the difference between software engineering and computer science?
    Computer science focuses on theory and fundamentals; software engineering is concerned with the practicalities of developing and delivering useful software.
  • 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 more general process.
  • What are the key challenges facing software engineering?
    Coping with increasing diversity, demands for reduced delivery times and developing trustworthy software.
  • What are the costs of software engineering?
    Roughly 60% of software costs are development costs, 40% are testing costs. For custom software, evolution costs often exceed development costs.
  • What are the best software engineering techniques and methods?
    While all software projects have to be professionally managed and developed, different techniques are appropriate for different types of system. For example, games should always be developed using a series of prototypes whereas safety critical control systems require a complete and analysable specification to be developed. You can’t, therefore, say that one method is better than another.
  • What differences has the web made to software engineering?
    The web has led to the availability of software services and the possibility of developing highly distributed service based systems. Web-based systems development has led to important advances in programming languages and software reuse.

What is Software?

  • Software is a set of items or objects that form a “configuration” that includes
    • Programs
    • Documents
    • data …
  • Software products may be developed for a particular customer or may be developed for a general market

Software Products

  • Generic products
    • Stand-alone systems that are marketed and sold to any customer who wishes to buy them.
    • Examples – PC software such as graphics programs, project management tools; CAD software; software for specific markets such as appointments systems for dentists.
  • Customized products
    • Software that is commissioned by a specific customer to meet their own needs.
    • Examples – embedded control systems, air traffic control software, traffic monitoring systems.

Product Specification

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

Essential attributes of good software

  • Maintainability (Characteristic)
    Description – 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 security (Characteristic)
    Description – Software dependability includes a range of characteristics including 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 (Characteristic)
    Description – 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 (Characteristic)
    Description – 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.


  • First computers were built in the mid-1940s.
  • 1960s realisation programming techniques had lagged behind developments in software both in size and complexity. Programming was an art not a craft, programmers had learned by doing. They had not been formally educated.
  • Result software was delivered late, programs behaved unexpectedly and were difficult to change, many errors were detected after delivery – “the software crisis”
  • 1968/69 NATO conferences: introduction of the term Software Engineering
    • Idea: software development is not an art, or a bag of tricks
    • Build software like we build bridges starting from a sound theoretical basis using proven design and construction techniques.

What is Software Engineering?

  • Software engineering is an engineering discipline which is 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.
  • 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.
  • Software engineering is concerned with theories, methods and tools for professional software development

Software Engineering

  • Engineering discipline
    Using appropriate theories and methods to solve problems bearing in mind organizational and financial constraints.
  • All aspects of software production
    Not just technical process of development. Also project management and the development of tools, methods etc. to support software production.

Software Engineering IEEE

  • Software Engineering
  • (1) The application of a systematic, disciplined, quantifiable approach to the development operation and maintenance of software; that is, the application of engineering to software. (2) The study of approaches as in (1).

The Problem

The quality of the systems we develop increasingly determines the quality of our existence.

“For a short period last Tuesday, the United States brought their atomic bombers and nuclear missiles to an increased state of alarm when, because of a computer error, a false alarm indicated that the Soviet Union had started a missile attack.” – 6 June 1980. The engines of the planes of the strategic air force were started three days later due to the same error.

The world is not always in danger
April 2008 Aer Lingus website mistakenly sold 1,775 euro business class tickets to the US for 5 euro.
September 2009 Bank of Ireland charged customers twice for each laser transaction on Friday September 4th
July 2012 Ulster Bank
Summer 2014 Delayed payment of public sector salaries

Characteristics of Software Engineering

  • Concerns the development of large programs – multi-person jobs that span more than six months.
  • Complexity is an issue – the problem cannot be surveyed in its entirety but must be broken down into smaller more manageable parts.
  • Software evolves- with associated costs.
  • Software must be developed efficiently.
  • Many people are working together.
  • The software must effectively support users.
  • Is a field in which members of one culture create artefacts on behalf of members of another.

Building Software – Building Bridges?


  • In both cases we work from a set of desired functions using scientific and engineering techniques in a creative way.
  • Techniques for development of physical artefacts can be applied to the construction of software systems:
    – Phased development
    – Careful planning of each phase
    – Continuous audit of the whole process
    – Construction from a clear and complete design

And No

  • The cost of constructing software is incurred during development and not production. Copying of software is free
  • Software is logical, rather than physical it does not wear out.
  • Software reliability is determined by the manifestation of errors already present not wear and tear.
  • Often we are not dealing with a well defined problem and the design process is open ended with the problem emerging as work progresses.
  • Progress is hard to see (speed ¹ progress). n Software is not continuous – small changes in the specification can lead to considerable changes in the product. In 1998 the Mars Climate Orbiter got lost because one team used English units while the other used metric.

Importance of Software 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 rather than just write the programs as if it was a personal programming project. For most types of system, the majority of costs are the costs of changing the software after it has gone into use.

Phases in the Development of Software

  • The need to ‘engineer’ the software process has long been recognised. The area of software process modelling has emerged as an increasingly more formal, or at least disciplined way of doing this.
  • Management must understand the need for a solid foundation prior to embarking on the actual development of any software.

Software Process Activities

  • Software specification, where customers and engineers define the software that is to be produced and the constraints on its operation.
  • Software development, where the software is designed and programmed.
  • Software validation, where the software is checked to ensure that it is what the customer requires.
  • Software evolution, where the software is modified to reflect changing customer and market requirements.

Software Process

  • Is a framework for carrying out the activities of a project in an organised and disciplined manner.
  • It imposes structure and helps guide the many people and activities in a coherent manner. Expresses the interrelationships among the phases by defining their order and frequency, as well as deliverables.
  • Different types of systems need different development processes

General Issues That Affect 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.

Software Engineering Diversity

  • There are many different types of software system and there is no universal set of software techniques that is applicable to all of these.
  • The software engineering methods and tools used depend on the type of application being developed, the requirements of the customer and the background of the development team.

Application Types

  • Stand-alone applications
    – These are application systems that run on a local computer, such as a PC. They include all necessary functionality and do not need to be connected to a network.
  • Interactive transaction-based applications
    – Applications that execute on a remote computer and are accessed by users from their own PCs or terminals. These include web applications such as e-commerce applications.
  • Embedded control systems
    – These are software control systems that control and manage hardware devices. Numerically, there are probably more embedded systems than any other type of system.
  • 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
    – These are systems that are primarily for personal use and which are intended to entertain the user.
  • Systems for modeling and simulation
    – These are systems that are developed by scientists and engineers to model physical processes or situations, which include many, separate, interacting objects.
  • Data collection systems
    – These are systems that collect data from their environment using a set of sensors and send that data to other systems for processing.
  • Systems of systems
    – These are systems that are composed of a number of other software systems.

Key Challenges Facing Software Engineering

  • Coping with legacy systems, coping with increasing diversity and coping with demands for reduced delivery times.
  • Legacy systems
    – Old, valuable systems must be maintained and updated.
  • Heterogeneity
    – Systems are distributed and include a mix of hardware and software.
  • Delivery
    – There is increasing pressure for faster delivery of software.

Recent Developments

  • Rise of agile methods.
  • Shift from producing software to using software – assemble systems from existing components.
  • Success of Open Source Software.
  • Software development becomes more heterogeneous.
    – Teams scattered around the globe
    – Components acquired from others
    – Includes open source parts
    – Services found on the Web

Software Engineering

  • Software is essential in our day-to-day life, we rely on complex computer based systems.
  • Many products incorporate computers and controlling software.
  • Software in these systems represent a large and increasing proportion of software costs.
  • The goal of software engineering is the creation of software systems that meet the needs of customers and are reliable, efficient and maintainable.
  • In the early days the field was seen as an art and in a counter movement the term “software engineering” was coined.
  • In the 1990s the pendulum swung back and the art aspect was emphasised anew in the agile movement.

Software Engineering Ethics

  • Like other disciplines, software engineering is carried out within a legal and social framework that limits the freedom of engineers. Two bodies the IEEE Computer Society and ACM have jointly developed a software engineering code of practice which can be found at:
  • acm.org/about/se-code
  • 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.

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.
  • 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).

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.

Rationale for the Code of Ethics

Computers have a central and growing role in commerce, industry, government, medicine, education, entertainment and society at large. Software engineers are those who contribute by direct participation or by teaching, to the analysis, specification, design, development, certification, maintenance and testing of software systems.

Because of their roles in developing software systems, software engineers have significant opportunities to do good or cause harm, to enable others to do good or cause harm, or to influence others to do good or cause harm. To ensure, as much as possible, that their efforts will be used for good, software engineers must commit themselves to making software engineering a beneficial and respected profession.

The ACM/IEEE Code of Ethics

Software Engineering Code of Ethics and Professional Practice

ACM/IEEE-CS Joint Task Force on Software Engineering Ethics and Professional Practices

The short version of the code summarizes aspirations at a high level of the abstraction; the clauses that are included in the full version give examples and details of how these aspirations change the way we act as software engineering professionals. Without the aspirations, the details can become legalistic and tedious; without the details, the aspirations can become high sounding but empty; together, the aspirations and the details form a cohesive code.

Software engineers shall commit themselves to making the analysis, specification, design, development, testing and maintenance of software a beneficial and respected profession. In accordance with their commitment to the health, safety and welfare of the public, software engineers shall adhere to the following Eight Principles:

Software Engineering Ethics – Principles

  • Act consistently with the public interest
  • Act in a manner that is in the best interest of the client and employer
  • Ensure that products meet the highest professional standards possible
  • Maintain integrity in professional judgment
  • Managers shall promote an ethical approach
  • Advance the integrity and reputation of the profession
  • Be fair to and supportive of colleagues
  • Participate in lifelong learning and promote an ethical approach

Ethical Principles

  1. PUBLIC – Software engineers shall act consistently with the public interest.
  2. 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.
  3. PRODUCT – Software engineers shall ensure that their products and related modifications meet the highest professional standards possible.
  4. JUDGMENT – Software engineers shall maintain integrity and independence in their professional judgment.
  5. MANAGEMENT – Software engineering managers and leaders shall subscribe to and promote an ethical approach to the management of software development and maintenance.
  6. PROFESSION – Software engineers shall advance the integrity and reputation of the profession consistent with the public interest.
  7. COLLEAGUES – Software engineers shall be fair to and supportive of their colleagues.
  8. 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.
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