An Introduction to Software Engineering

1 Ian Sommerville 2004 Software Engineering , 7th edition. Chapter 1 Slide 1An Introduction to SoftwareEngineering Ian Sommerville 2004 Software Engineering , 7th edition. Chapter 1 Slide 2 Objectives 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 Ian Sommerville 2004 Software Engineering , 7th edition. Chapter 1 Slide 3 Topics covered FAQs about Software Engineering Professional and ethical responsibility Ian Sommerville 2004 Software Engineering , 7th edition. Chapter 1 Slide 4 Software Engineering The economies of ALL developed nations aredependent on Software . More and more systems are Software controlled Software Engineering is concerned with theories,methods and tools for professional softwaredevelopment.

2 Expenditure on Software represents asignificant fraction of GNP in all developedcountries. Ian Sommerville 2004 Software Engineering , 7th edition. Chapter 1 Slide 5 Software 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 long life,maintenance costs may be several timesdevelopment costs. Software Engineering is concerned with cost-effective Software development. Ian Sommerville 2004 Software Engineering , 7th edition. Chapter 1 Slide 6 FAQs 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? Ian Sommerville 2004 Software Engineering , 7th edition.

3 Chapter 1 Slide 7 FAQs 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? Ian Sommerville 2004 Software Engineering , 7th edition. Chapter 1 Slide 8 What 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 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 .

4 Ian Sommerville 2004 Software Engineering , 7th edition. Chapter 1 Slide 9 What 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. Ian Sommerville 2004 Software Engineering , 7th edition. Chapter 1 Slide 10 What 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 physics and electricalengineering). Ian Sommerville 2004 Software Engineering , 7th edition.

5 Chapter 1 Slide 11 What 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. Ian Sommerville 2004 Software Engineering , 7th edition. Chapter 1 Slide 12 What 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.

6 Ian Sommerville 2004 Software Engineering , 7th edition. Chapter 1 Slide 13 What is a Software process model? A simplified representation of a Software process,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 . Ian Sommerville 2004 Software Engineering , 7th edition. Chapter 1 Slide 14 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 systembeing developed and the requirements of systemattributes such as performance and systemreliability. Distribution of costs depends on thedevelopment model that is used.

7 Ian Sommerville 2004 Software Engineering , 7th edition. Chapter 1 Slide 15 Activity cost distribution Ian Sommerville 2004 Software Engineering , 7th edition. Chapter 1 Slide 16 Product development costs Ian Sommerville 2004 Software Engineering , 7th edition. Chapter 1 Slide 17 What 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. Ian Sommerville 2004 Software Engineering , 7th edition. Chapter 1 Slide 18 What is CASE (Computer-Aided SoftwareEngineering) Software systems that are intended to provide automatedsupport for Software process activities.

8 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 as programming,debugging and testing. Ian Sommerville 2004 Software Engineering , 7th edition. Chapter 1 Slide 19 What are the attributes of good Software ? The Software should deliver the required functionality andperformance to the user and should be maintainable,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 means it must be understandable, usable and compatiblewith other systems. Ian Sommerville 2004 Software Engineering , 7th edition. Chapter 1 Slide 20 What are the key challenges facing softwareengineering?

9 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. Ian Sommerville 2004 Software Engineering , 7th edition. Chapter 1 Slide 21 Professional 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. Ian Sommerville 2004 Software Engineering , 7th edition. Chapter 1 Slide 22 Issues of professional responsibility Confidentiality Engineers should normally respect the confidentialityof their employers or clients irrespective of whetheror not a formal confidentiality agreement has beensigned.

10 Competence Engineers should not misrepresent their level ofcompetence. They should not knowingly accept workwhich is outwith their competence. Ian Sommerville 2004 Software Engineering , 7th edition. Chapter 1 Slide 23 Issues 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 s machine,say) to extremely serious (dissemination of viruses). Ian Sommerville 2004 Software Engineering , 7th edition. Chapter 1 Slide 24 ACM/IEEE Code of Ethics The professional societies in the US havecooperated to produce a code of ethical practice.