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0273710133 pp01v2

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  • 1. ©Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 1 Slide 1An Introduction to SoftwareEngineering
  • 2. ©Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 1 Slide 2Objectives To introduce software engineering and to explainits importance To set out the answers to key questions aboutsoftware engineering To introduce ethical and professional issues andto explain why they are of concern to softwareengineers
  • 3. ©Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 1 Slide 3Topics covered FAQs about software engineering Professional and ethical responsibility
  • 4. ©Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 1 Slide 4Software engineering The economies of ALL developed nations aredependent on software. More and more systems are software controlled Software engineering is concerned withtheories, methods and tools for professionalsoftware development. Expenditure on software represents asignificant fraction of GNP in all developedcountries.
  • 5. ©Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 1 Slide 5Software costs Software costs often dominate computer systemcosts. The costs of software on a PC are oftengreater than the hardware cost. Software costs more to maintain than it does todevelop. For systems with a longlife, maintenance costs may be several timesdevelopment costs. Software engineering is concerned with cost-effective software development.
  • 6. ©Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 1 Slide 6FAQs about software engineering What is software? What is software engineering? What is the difference between softwareengineering and computer science? What is the difference between softwareengineering and system engineering? What is a software process? What is a software process model?
  • 7. ©Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 1 Slide 7FAQs about software engineering What are the costs of software engineering? What are software engineering methods? What is CASE (Computer-Aided SoftwareEngineering) What are the attributes of good software? What are the key challenges facing softwareengineering?
  • 8. ©Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 1 Slide 8What is software? Computer programs and associated documentation suchas requirements, design models and user manuals. Software products may be developed for a particularcustomer or may be developed for a general market. Software products may be• Generic - developed to be sold to a range of different customerse.g. PC software such as Excel or Word.• Bespoke (custom) - developed for a single customer accordingto their specification. New software can be created by developing newprograms, configuring generic software systems orreusing existing software.
  • 9. ©Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 1 Slide 9What is software engineering? Software engineering is an engineering disciplinethat is concerned with all aspects of softwareproduction. Software engineers should adopt a systematicand organised approach to their work and useappropriate tools and techniques depending onthe problem to be solved, the developmentconstraints and the resources available.
  • 10. ©Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 1 Slide 10What is the difference between softwareengineering and computer science? Computer science is concerned with theory andfundamentals; software engineering is concernedwith the practicalities of developing anddelivering useful software. Computer science theories are still insufficient toact as a complete underpinning for softwareengineering (unlike e.g. physics and electricalengineering).
  • 11. ©Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 1 Slide 11What is the difference between softwareengineering and system engineering? System engineering is concerned with allaspects of computer-based systemsdevelopment including hardware, software andprocess engineering. Software engineering ispart of this process concerned with developingthe software infrastructure, control, applicationsand databases in the system. System engineers are involved in systemspecification, architectural design, integrationand deployment.
  • 12. ©Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 1 Slide 12What 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 itsdevelopment constraints• Development - production of the software system• Validation - checking that the software is what thecustomer wants• Evolution - changing the software in response tochanging demands.
  • 13. ©Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 1 Slide 13What is a software process model? A simplified representation of a softwareprocess, presented from a specific perspective. Examples of process perspectives are• Workflow perspective - sequence of activities;• Data-flow perspective - information flow;• Role/action perspective - who does what. Generic process models• Waterfall;• Iterative development;• Component-based software engineering.
  • 14. ©Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 1 Slide 14What are the costs of software engineering? Roughly 60% of costs are developmentcosts, 40% are testing costs. For customsoftware, evolution costs often exceeddevelopment costs. Costs vary depending on the type of systembeing developed and the requirements of systemattributes such as performance and systemreliability. Distribution of costs depends on thedevelopment model that is used.
  • 15. ©Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 1 Slide 15Activity cost distributionWaterfall modelIterative developmentComponent-based software eng ineeringDevelopment and evolution costs for long-lifetime syst emsSystemevolution10 200 30 4000SystemdevelopmentSpecification Design Development Integration and testing25 50 75 1000Specification Development Integration and testing25 50 75 1000Specification Iterative development Systemtesting25 50 75 1000
  • 16. ©Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 1 Slide 16Product development costsSpecification Development Systemtesting25 50 75 1000
  • 17. ©Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 1 Slide 17What are software engineering methods? Structured approaches to software development whichinclude system models, notations, rules, design adviceand process guidance. 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.
  • 18. ©Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 1 Slide 18What is CASE (Computer-Aided SoftwareEngineering) Software systems that are intended to provide automatedsupport for software process activities. CASE systems are often used for method support. Upper-CASE• Tools to support the early process activities of requirementsand design; Lower-CASE• Tools to support later activities such asprogramming, debugging and testing.
  • 19. ©Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 1 Slide 19What are the attributes of good software? The software should deliver the required functionality andperformance to the user and should bemaintainable, dependable and acceptable. Maintainability• Software must evolve to meet changing needs; Dependability• Software must be trustworthy; Efficiency• Software should not make wasteful use of system resources; Acceptability• Software must accepted by the users for which it was designed.This means it must be understandable, usable and compatiblewith other systems.
  • 20. ©Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 1 Slide 20What are the key challenges facing softwareengineering? Heterogeneity, delivery and trust. Heterogeneity• Developing techniques for building software that can cope withheterogeneous platforms and execution environments; Delivery• Developing techniques that lead to faster delivery of software; Trust• Developing techniques that demonstrate that software can betrusted by its users.
  • 21. ©Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 1 Slide 21Professional and ethical responsibility Software engineering involves widerresponsibilities than simply the application oftechnical skills. Software engineers must behave in an honestand ethically responsible way if they are to berespected as professionals. Ethical behaviour is more than simply upholdingthe law.
  • 22. ©Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 1 Slide 22Issues of professional responsibility Confidentiality• Engineers should normally respect the confidentialityof their employers or clients irrespective of whetheror not a formal confidentiality agreement has beensigned. Competence• Engineers should not misrepresent their level ofcompetence. They should not knowingly accept workwhich is outwith their competence.
  • 23. ©Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 1 Slide 23Issues of professional responsibility Intellectual property rights• Engineers should be aware of local laws governing the use ofintellectual property such as patents, copyright, etc. Theyshould be careful to ensure that the intellectual property ofemployers and clients is protected. Computer misuse• Software engineers should not use their technical skills tomisuse other people’s computers. Computer misuse rangesfrom relatively trivial (game playing on an employer’smachine, say) to extremely serious (dissemination of viruses).
  • 24. ©Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 1 Slide 24ACM/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 thebehaviour of and decisions made by professionalsoftware engineers, includingpractitioners, educators, managers, supervisorsand policy makers, as well as trainees andstudents of the profession.
  • 25. ©Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 1 Slide 25Code of ethics - preamble Preamble• The short version of the code summarizes aspirations at a highlevel of the abstraction; the clauses that are included in the fullversion give examples and details of how these aspirationschange the way we act as software engineering professionals.Without the aspirations, the details can become legalistic andtedious; without the details, the aspirations can become highsounding but empty; together, the aspirations and the detailsform a cohesive code.• Software engineers shall commit themselves to making theanalysis, specification, design, development, testing andmaintenance of software a beneficial and respected profession.In accordance with their commitment to the health, safety andwelfare of the public, software engineers shall adhere to thefollowing Eight Principles:
  • 26. ©Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 1 Slide 26Code 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.
  • 27. ©Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 1 Slide 27Code of ethics - principles JUDGMENT• Software engineers shall maintain integrity and independencein their professional judgment. MANAGEMENT• 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.
  • 28. ©Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 1 Slide 28Code of ethics - principles COLLEAGUES• Software engineers shall be fair to and supportive oftheir colleagues. SELF• Software engineers shall participate in lifelonglearning regarding the practice of their professionand shall promote an ethical approach to the practiceof the profession.
  • 29. ©Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 1 Slide 29Ethical dilemmas Disagreement in principle with the policies ofsenior management. Your employer acts in an unethical way andreleases a safety-critical system without finishingthe testing of the system. Participation in the development of militaryweapons systems or nuclear systems.
  • 30. ©Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 1 Slide 30Key points Software engineering is an engineering discipline that isconcerned with all aspects of software production. Software products consist of developed programs andassociated documentation. Essential product attributesare maintainability, dependability, efficiency and usability. The software process consists of activities that areinvolved in developing software products. Basic activitiesare software specification, development, validation andevolution. Methods are organised ways of producing software. Theyinclude suggestions for the process to be followed, thenotations to be used, rules governing the systemdescriptions which are produced and design guidelines.
  • 31. ©Ian Sommerville 2006 Software Engineering, 8th edition. Chapter 1 Slide 31Key points CASE tools are software systems which are designed tosupport routine activities in the software process such asediting design diagrams, checking diagram consistencyand keeping track of program tests which have been run. Software engineers have responsibilities to theengineering profession and society. They should notsimply be concerned with technical issues. Professional societies publish codes of conduct which setout the standards of behaviour expected of theirmembers.