Objectives of the Lecture To introduce software engineering and to explain its importance in dealing with large software systems. To provide answers to key questions about software design and development as part of software engineering discipline.

Software systems The impact of software systems on modern society and technology for 50 years. Process automation: automobile industry; refinery; software product family for electronic devices; telephony and switching systems Equipment control: embedded systems in different electronic devices such as home appliances; automobile control gadgets Scientific problems: differential equations; matrix operations; model checking; searching algorithms; information system manipulation Entertainment industry: gaming; graphics; movies; music Education and office management: distance education; word processors; databases; spreadsheets; slide presenters Software systems are around for more than 50 years. They are implemented to assist human in different aspects of their lives such as: process……

Software systems … Example of very large software systems Flight simulators; medical and imaging applications; air-traffic control; banking; telecommunications; etc. These systems are written in more than 500 different languages. Billions of lines of source code are written for mission critical software systems worldwide. process automation: automobile industry; product families; refineries; .. Equipment control: embedded systems in different electronic devices

Software engineering to solve software crisis Software crisis refers to the current state of software technology in dealing with development and maintenance of large and complex software systems. Instances are: For every 8 large projects, 2 are cancelled. Most projects exceed their time-schedule by 50%. 75% of large software systems malfunction after completion. Detecting and correcting errors take 50% of time and effort. Maintenance cost of a system is 60% of entire cost. An example: baggage-handling system at Denver international airport 4000 telecars, 5000 electric-eyes, 400 radio receivers, 100 computers, cost $193 million Discuss the cause of each instance of software crisis: Project management Project management and lack of understanding of the problem Lack of accurate software specification Errors that are left in the system since the development was not standard and precise Errors that remained in the system from beginning that is requirement specification SRS The grand opening of the airport was delayed for 9 months because the baggage conveyer belt did not work properly, and had high speed at in the curves that caused the luggage's to be thrown out of the conveyer belt. It cost one-million dollar per day for the airport because of delay in operation. Software engineering tackles the software crisis by providing disciplined processes and methodologies to design, implement, and maintain large systems.

Software engineering key questions 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? What is a software process model?

Software engineering… 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?

What is software? Computer programs and associated documentation: SRS, SDS, Technical manual, User manual, Source code, Binary files, Build files, Versions Tool provided documents: Reverse Engineering aspects, Tracing code to requirement Software products may be Generic - developed to be sold to a range of different customers Customized - developed for a single customer according to their specification

What is software engineering? “Multi-person construction of multi-version software” [Parnas 1978] 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

Professional Responsibilities of Software Engineers Accept individual responsibility Solve the real problem Be honest about capabilities and competence Produce reviewable designs Consider maintainability of product Respect to confidentiality of the clients Knowledge of IP rights for patents, copyright, etc. No computer miss-use by e.g., computer games; spreading computer viruses P.Eng. Applicants write Ethics and Law Exams

What is the difference between software engineering and computer science? 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 Computer science: * Theory: design of algorithms, complexity of the computations; computational geometry; * System: databases, distributed systems; web technology; * Scientific computation; computer graphics; * Software Engineering deals with the appropriate methodologies, techniques, and tools to design or analysis of large software systems. : reverse engineering; forward engineering; formal methods and tools

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 process System engineers are involved in system specification, architectural design, integration and deployment

What is a software process? A set of activities whose goal is the development or evolution of software Generic activities in all software processes are: 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

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 Evolutionary development Formal transformation Integration from reusable components

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 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

What are software engineering methods? Structured approaches to software development which include system models, notations, rules, design advice and 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

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

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

What are the 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