1 Introduction to Software Engineering Objectives l l

1. Introduction to Software Engineering Objectives l l l To introduce software engineering and to explain its importance To set out the answers to key questions about software engineering To introduce ethical and professional issues and to explain why they are of concern to software engineers 1

Software engineering l l 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 Software engineering expenditure represents a significant fraction of GNP in all developed countries 2

Software costs l l l 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 costeffective software development 3

FAQs about software engineering l l l What is software? What is software engineering? What is the difference between software engineering and computer science? What is the difference between software engineering and system engineering? What is a software process model? 4

FAQs about software engineering l l l What are the costs of software engineering? What are software engineering methods? What is CASE (Computer-Aided Software Engineering) What are the attributes of good software? What are the key challenges facing software engineering? 5

What is software? l Computer programs and associated documentation l Software products may be developed for a particular customer or may be developed for a general market Software products may be l l l Generic - developed to be sold to a range of different customers Bespoke (custom) - developed for a single customer according to their specification 6

What is software engineering? q IEEE Definition (1993) “The application of a systematic, disciplines, quantifiable approach to the development, operation, and maintenance of software; that is the application of engineering to software. ” l l Software engineering is an engineering discipline which is concerned with all aspects of software production 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 7

What is the difference between software engineering and computer science? l l Computer science is concerned with theory and fundamentals; software engineering is concerned with the practicalities of developing and delivering useful software Computer science theories are currently insufficient to act as a complete underpinning for software engineering 8

WHERE DOES SOFTWARE ENGINEERING FIT IN? COMPUTER SCIENCE Theories CUSTOMER Computer Functions Problem SOFTWARE ENGINEERING Tools and Techniques to Solve Problem 9

What is the difference between software engineering and system engineering? l l System engineering is concerned with all aspects of computer-based systems development including hardware, software and process engineering. Software engineering is part of this process System engineers are involved in system specification, architectural design, integration and deployment 10

What is a software process? l l A set of activities whose goal is the development or evolution of software Generic activities in all software processes are: l l Specification - what the system should do and its development constraints Development - production of the software system Validation - checking that the software is what the customer wants Evolution - changing the software in response to changing demands 11

What is a software process model? l l A simplified description of a software process that presents one view of that process Examples of s/w process model: l l Workflow model - sequence of activities Data-flow /activity model - information flow Role/action model - who does what Generic process models l l l Waterfall approach Iterative development Component based s/w engineering 12

What are the costs of software engineering? l l l 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 system being developed and the requirements of system attributes such as performance and system reliability Distribution of costs depends on the development model that is used 13

What are software engineering methods? l l l Structured approaches to software development Component of s/w eng methods: System models l l Rules l l Constraints applied to system models Recommendations l l Descriptions of graphical models which should be produced Advice on good design practice Process guidance l What activities to follow 14

What is CASE (Computer-Aided Software Engineering) l l Software systems which are intended to provide automated support for software process activities. CASE systems are often used for method support Upper-CASE l l Tools to support the early process activities of requirements and design Lower-CASE l Tools to support later activities such as programming, debugging and testing 15

What are the attributes of good software? l The software should deliver the required functionality and performance to the user and should be maintainable, dependable and usable l Maintainability l l Dependability l l Software must be trustworthy Efficiency l l Software must evolve to meet changing needs Software should not make wasteful use of system resources Usability l Software must be usable by the users for which it was designed 16

What are the key challenges facing software engineering? l Trust l l Heterogeneity l l Develop techniques that demonstrate s/w can be trusted by its user Challenge of developing techniques for building dependable s/w Delivery l There is increasing pressure for faster delivery of software 17

Professional and ethical responsibility l l l 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. 18

Issues of professional responsibility l Confidentiality l l Engineers should normally respect the confidentiality of their employers or clients irrespective of whether or not a formal confidentiality agreement has been signed. Competence l Engineers should not misrepresent their level of competence. They should not knowingly accept work which is outwith their competence. 19

Issues of professional responsibility l Intellectual property rights l l 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 l 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). 20

ACM/IEEE Code of Ethics l l l 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. 21

Code of ethics - principles l 1. PUBLIC l l 2. CLIENT AND EMPLOYER l l Software engineers shall act consistently with the public interest. 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 l Software engineers shall ensure that their products and related modifications meet the highest professional standards possible. 22

Code of ethics - principles l 4. JUDGMENT l l 5. MANAGEMENT l l Software engineers shall maintain integrity and independence in their professional judgment. Software engineering managers and leaders shall subscribe to and promote an ethical approach to the management of software development and maintenance. 6. PROFESSION l Software engineers shall advance the integrity and reputation of the profession consistent with the public interest. 23

Code of ethics - principles l 7. COLLEAGUES l l Software engineers shall be fair to and supportive of their colleagues. 8. SELF l 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. 24

Ethical dilemmas l l l 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 25

Software Rejuvenation l Is a proactive fault management technique aimed at cleaning up the system internal state to prevent the occurrence of more severe crash failures in the future 26

Software Reengineering l What? Restructuring or re-writing part or all of a legacy system without changing its functionality l When? When some but not all sub-system of a larger system require frequent maintenance l When h/w @ s/w support becomes obsolete l How ? The system may be re-structured and re-documented to make it easier to maintain l Why ? Reduced risk New s/w development carries high risk Reduced cost § The cost of re-engineering is often significantly less than the costs of developing new s/w § 27

Forward engineering & reengineering System Specification Design & Implementation New System Understanding & transformation Re-engineered system Forward engineering Existing software system Software re-engineering Automated program conversion Automated program restructuring Manual program & data restructuring Restructuring plus architectural changes 28

l Reengineering a software system has 2 key advantages over more radical approaches to system evolution l l reduced risk: there is a high risk in redeveloping s/w that is essential for an organization. Errors may be made in the system specification, they maybe development problems reduce cost: the cost of re-engineering is significantly less than the cost of developing new software 29

Reverse engineering l l l l Analyzing s/w to gain understanding of its design and specification May be part of re-engineering process or to re-specify a system for re-implementation Build a program database and generates information from this Program understanding tools (browser, cross-reference generators, etc) may be used in this process Why? original code may be have been written under limitation which no longer apply e. g: memory needs, performance etc Maintenance tends to corrupt the structure of a program. It becomes harder and harder to understand The program may be automatically restructured to remove unconditional branches or complex conditional statements 30

The re-engineering process Program documentation Original program modularized program Original data Reverse engineering Program modularization Datareengineering Source code translation Program Source code structure translation improvement structured program Reengineered data 31

Activities in re-engineering process l l l Source code translation: the program is converted from an old programs language to a more modern version of the same language/to a different language Reverse engineering: the program is analyzed, information extracted from it which helps to document its organization and functionality Program structure improvement: the control structure of the program is analyzed and modified to make it easier to read and understand Program modularization: related part of the program are grouped together and where appropriate, redundancy is remove. In some cases this stage may involved architectural transformation Data re-engineering: the data processed by the program is changed to reflect program changes 32