ch1_introduction (1).ppt
- 1. 1 Chapter 1: Introduction to Software Engineering Chapter 1 in Software Engineering Book
- 2. 2 Overview ο¨ Learning Objectives. ο¨What is software engineering? ο¨ Why is software engineering important?
- 3. 3 By the end of this chapter, you will... ο¨Understand what software engineering is. ο¨ Understand why software engineering is important. ο¨ Know answers to key questions related to the software engineering discipline.
- 4. 4 Activity Think about all the devices and systems that you encounter in your everyday life which have software controlling them⦠List as many as you can Virtually all countries depend on complex computer-based systems.
- 5. 5 Why is Software Engineering important? Complex systems need a disciplined approach for designing, developing and managing them.
- 6. 6 Software Development Crises Projects were: β’ Late. β’ Over budget. β’ Unreliable. β’ Difficult to maintain. β’ Performed poorly.
- 7. 7 Software errorsβ¦.the cost Errors in computer software can have devastating effects.
- 8. 8 Software Crisis Example 1: 2009,Computer glitch delays flights Saturday 3rd October 2009-London, England (CNN) β’ Dozens of flights from the UK were delayed Saturday after a glitch in an air traffic control system in Scotland, but the problem was fixed a few hours later. β’ The agency said it reverted to backup equipment as engineering worked on the system. β’ The problem did not create a safety issue but could cause delays in flights. β’ Read more at: http://edition.cnn.com/2009/WORLD/europe/10/03/uk.fl ights.delayed
- 9. 9 Software Crisis Example 2: Ariane 5 Explosion β’ European Space Agency spent 10 years and $7 billion to produce Ariane 5. β’ Crash after 36.7 seconds. β’ Caused by an overflow error. Trying to store a 64-bit number into a 16-bit space. β’ Watch the video: http://www.youtube.com/watch?v=z-r9cYp3tTE
- 10. 10 Software Crisis Example 3: 1992, London Ambulance Service β’ Considered the largest ambulance service in the world. β’ Overloaded problem. β’ It was unable to keep track of the ambulances and their statuses. Sending multiple units to some locations and no units to other locations. β’ Generates many exceptions messages. β’ 46 deaths.
- 11. 11 Therefore⦠A well-disciplined approach to software development and management is necessary. This is called engineering.
- 12. 12 Software Engineering ο¨ The term software engineering first appeared in the 1968 NATO Software Engineering Conference and was meant to provoke thought regarding what was then called the βsoftware crisisβ.. ο¨ β.. An engineering discipline that is concerned with all aspects of software production from the early stages of system specification to maintaining the system after it has gone into use.β Sommerville, pg.7
- 13. Software Programs Documentation Data 13 What is Software? System Documentation User Documentation
- 14. 14 Types of Software β’ Generic products. β’ Stand-alone systems that are marketed and sold to any customer who wishes to buy them. β’ Examples β PC software such as graphics programs, project management tools; CAD software; software for specific markets such as appointments systems for dentists. β’ The specification of what the software should do is owned by the software developer and decisions on software change are made by the developer. β’ Customized or bespoke products. β’ Software that is commissioned by a specific customer to meet their own needs. β’ Examples β embedded control systems, air traffic control software, traffic monitoring systems. β’ The specification of what the software should do is owned by the customer for the software and they make decisions on software changes that are required.
- 15. 15 Software Engineering vs. Computer Science βComputer science is no more about computers than astronomy is about telescopes.β Edsger Dijkstra Computer Science β’ Theory. β’ Fundamentals. Software Engineering β’ Practicalities of software design, development and delivery.
- 16. 16 Software Engineering vs. Systems Engineering Systems Engineering: ο¨ Interdisciplinary engineering field (computer, software, and process eng.). ο¨ Focuses on how complex engineering projects should be designed and managed. Systems Engineering β’ All aspects of computer- based systems development: HW + SW + Process. β’ Older than SWE. Software Engineering β’ Deals with the design, development and delivery of SW. β’ Is part of Systems Engineering.
- 17. 17 Question Answer What is software? Computer programs and associated documentation. Software products may be developed for a particular customer or may be developed for a general market. What are the attributes of good software? Good software should deliver the required functionality and performance to the user and should be maintainable, dependable and usable. What is software engineering? Software engineering is an engineering discipline that is concerned with all aspects of software production. What are the fundamental software engineering activities? Software specification, software development, software validation and software evolution. What is the difference between software engineering and computer science? Computer science focuses on theory and fundamentals; software engineering is concerned with the practicalities of developing and delivering useful software. 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 more general process. Frequently asked questions about software engineering
- 18. 18 Frequently asked questions about software engineering Question Answer What are the key challenges facing software engineering? Coping with increasing diversity, demands for reduced delivery times and developing trustworthy software. What are the costs of software engineering? Roughly 60% of software costs are development costs, 40% are testing costs. For custom software, evolution costs often exceed development costs. What are the best software engineering techniques and methods? While all software projects have to be professionally managed and developed, different techniques are appropriate for different types of system. For example, games should always be developed using a series of prototypes whereas safety critical control systems require a complete and analyzable specification to be developed. You canβt, therefore, say that one method is better than another. What differences has the web made to software engineering? The web has led to the availability of software services and the possibility of developing highly distributed service-based systems. Web-based systems development has led to important advances in programming languages and software reuse.
- 19. 19 What is a Software Process? ο¨ Activities and results that produce a software product: SW Process Activity What is going on there? Specification What does the customer need? What are the constraints? Development Design & programming. Validation Checking whether it meets requirements. Evolution Modifications (e.g. customer/market).
- 20. 20 What is a Software Process Model? ο¨ Description of the software process that represents one view, such as the activities, data or roles of people involved. Examples of views Focus onβ¦ Workflow Activities = human actions. What is input, output, and dependencies. Dataflow Activities = transformations of information. How the input is transformed into output. Role/Action What is the role of people involved in each step of the process?
- 21. 21 Software Process Models Waterfall approach Iterative development Component-Based Software Engineering CBSE assembled form existing components
- 22. 22 The Cost of Software Engineering ο¨ Depends on: ο¨ The process used, and ο¨ The type of software being developed. ο¨ Each generic approach has a different profile of cost distribution. ο¨ Roughly 60% of costs are development costs, 40% are testing costs. ο¨ For custom software, evolution costs often exceed development costs.
- 23. 23 Cost distribution Custom software development (Bespoke) Software Model Cost units Cost distribution Software development activity Waterfall Model 0 25 50 75 100 Specification Design Development Integration and testing Iterative Development 0 25 50 75 100 Specification Iterative Development System testing Component-based Software Engineering 0 25 50 75 100 Specification Development Integration and testing Development and evolution costs for long-lifetime systems 0 100 200 300 400 System development System evolution
- 24. 24 Cost distribution Generic software development Product development costs 0 25 50 75 100 Specification Development System testing
- 25. 25 What is CASE? ο¨ Computer Aided Software Engineering. ο¨ Programs that support: ο¨ Requirements analysis. ο¨ System modeling. ο¨ Debugging. ο¨ Testing.
- 26. 26 Attributes of good software ο¨ Functional attributes (performance; what the system does). ο¨ Non-functional attributes (quality; how the system does it). Product Characteristic Description Maintainability Evolution qualities such as Testability, extensibility. Dependability Reliability, security, safety. Efficiency Response time, processing time, memory utilization. Usability Easy to learn how to use the system by target users. Efficient to use the system by users to accomplish a task. Satisfying to use by intended users.
- 27. 27 Activity ο¨ What are the key attributes for.. Interactive game Banking system Cardiac monitor in an ICU unit Players, score, scenes, theme. Client accounts, stocks bonds, money transfers. heart rate, temperature, blood pressure.
- 28. 28 Challenges facing software engineering Challenge Why? Software needs to .. Heterogeneity Different computers, different platforms, different support systems. Cope with this variability. Delivery Businesses are more responsive ο supporting software needs to evolve as rapidly. Be delivered in shorter time without compromising quality. Trust Software is a part of many aspects of our lives (work, study, leisure). Demonstrate that it can be trusted by users.
- 29. 29 References ο PRESS&SUN-BULLETIN, The Binghamton Press Co., Binghamton, NY, October 1,1999. ο βSoftware Hell: Is there a way out?β, BUSINESS WEEK, December 6, 1999. ο IEEE Standards Collection: Software Engineering, IEEE standard 610.12-1990, IEEE 1993. ο Sommerville, Ian βSoftware Engineeringβ, 9th edition, Addison-Wesley.