An Introduction to Software Engineering Based on Ian Sommerville’s Software Engineering 8 th Ed. Slides by Denny Lin

Objectives Understand what Software Engineering is, and why it is important Answer fundamental questions about Software Engineering Introduce ethical and professional responsibility issues as they relate to computer scientists and software engineers

Questions about Software Engineering What is software? –Software includes source code, executable, and associated documentation such as requirements documents, design models, and user manuals –May be targeted for some general purpose (web browser, word processor, etc), or for a specific custom need –New software can be produced from scratch, by configuring generic software systems, or by reusing existing software

Questions about Software Engineering What is Software Engineering? –Software engineering is an engineering discipline that applies theories, methods, and tools to solve problems related to software production and maintenance –Software engineers strive to deliver high- quality software, on time and within budget

Questions about Software Engineering Why is Software Engineering Important? –Financial, security, and safety critical systems rely on software –Software mediates every aspect of our Internet experience –The economies of all developed nations are dependent on software –There is an increasing need to cost effectively develop high-quality software

Questions about Software Engineering What is the difference between Software Engineering and Computer Science? –Software engineering is concerned with producing usable software for today; computer science is concerned with finding fundamental truths about theoretical problems for posterity –Software engineering projects have fixed budgets and schedules; computer science projects have open-ended budgets and schedules –Software created by software engineers must evolve as user’s needs change; solutions created by Computer Scientists never change –Software engineers require domain knowledge to function; computer scientists rely on mathematical principles to function –Unlike physics and electrical engineering, software engineers often rely on methods and principles borrowed from other engineering disciplines instead of computer science

Questions about Software Engineering What is the difference between Software Engineering and System Engineering? –System Engineering is concerned with all aspects of computer based systems, including hardware, software and process engineering; applies tested and known principles; the discipline is thousands of years old –Software Engineering is concerned with developing the software infrastructure, control, applications, and databases in the system; often apply new and untested elements in software projects; the discipline is about 50 years old

Questions about Software Engineering What is a Software Process? –A software process is a set of activities and their output, which result in a software product –Four fundamental process activities are: Specification: Defines what the software should do, and its operational constraints Design and implementation: Designs the solutions, and produces the source code to meet the specification Validation: Checks that the software produced is what the customer wants Evolution: Changes made to the software that meet user’s changing needs

Questions about Software Engineering What is a Software Process model? –An abstract representation of a software process, presented from a particular perspective; for example, workflow (sequence of activities), data-flow (information flow), or role/action (who does what) –These process models explain different approaches to software development; for example, Waterfall, Iterative, and Component Based Software Engineering

Questions about Software Engineering What is the cost of Software? –Software costs often dominate computer system costs. –Software costs more to maintain than to develop from scratch. The maintenance costs for systems with a long-life, may be several times its development costs

Questions about Software Engineering What are the costs of Software Engineering? –Roughly 60% of costs are development costs, and 40% are testing costs. Evolution costs often exceed development costs in custom software –Costs vary depending on the type and requirements of system under development –The distribution of costs depend on the development model used

Activity Cost Distribution by Development Model

Product Development Costs for PCs

Questions about Software Engineering What are Software Engineering methods? –Structured approaches to software development, including: Model descriptions: Describes graphical models (i.e. object, data- flow, state machine models, etc) Rules: Constraints applied to system models (i.e. entities must have unique names) Recommendations: Best practices for designing software (i.e. include no more than nine processes in a data flow diagram) Process guidance: what activities to follow (i.e. document object attributes before defining its operations) –Examples of methods: Functional oriented: DeMarco’s Structured Analysis and Jackson’s JSD Object oriented: Booch, Rumbaugh, and Boehm’s Obejct Oriented methods, Rational Unified Process

Questions about Software Engineering What is CASE? –Computer Assisted Software Engineering, used to provide automated support for software process activities –Often used for method support –Upper-CASE tools support requirements gathering and design activities –Lower-CASE tools support implementation, debugging, and testing activities

Questions about Software Engineering What are the attributes of good software? –Software should deliver the functionality required by the user. In addition, it should deliver non-functional requirements such as: Maintainability: Must be easy to evolve to address changing needs Dependability: Must be trustworthy Efficiency: Should not waste system resources Acceptability: Users must be able to use the software

Questions about Software Engineering What are the key challenges facing software engineering? –Heterogeneity: How to build software that works on different platforms, that can integrate with older legacy systems which are written in different programming languages –Delivery: How to shorten the time it takes to deliver a finished software product, without compromising its quality –Trust: How to develop techniques to demonstrate that software can be trusted by its users

Professional and Ethical Responsibility Software engineering involves wider responsibilities than just the application of technical skills Software engineers must behave in honest and ethically responsible ways to be respected as professionals Ethical behavior is more than simply upholding the law

Two Ethical Perspectives on Reciprocity Confucian: “Never impose on others what you would not choose for yourself.” - Analects XV.24, tr. David Hinton ” Christian: “Just as you want others to do for you, do the same for them.” Luke 6:31

Issues of Professional Responsibility Confidentiality –Always respect confidentiality of employers or clients, even when there is no formal confidentiality agreement Competence –Never misrepresent one’s level of competence. Never accept work beyond one’s level of competence

Issues of Professional Responsibility Intellectual property rights –Ensure that the intellectual property of employers and clients is protected –Be aware of local laws governing use of intellectual property such as patents and copyright Computer misuse –Never use technical skills to misuse other people’s computers

ACM/IEEE Software Engineering Code of Ethics and Professional Practice See There is a short and long version of the code of ethics The Preamble explains the purpose of these two versions, the commitment of software engineers to make their discipline a respected profession, and to adhere to the eight principles for the health, safety, and welfare of the public.

Code of Ethics – Eight 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.

Code of Ethics – Eight Principles 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.

Code of Ethics – Eight Principles 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 policies of senior management Your employer acts unethically by releasing a safety-critical system without finishing the testing of the system You participate in the development of military weapons or nuclear systems You are coerced under threat to you or your family, to produce malware