Transcript Document
Introduction
ECE 417/617: Elements of Software Engineering Stan Birchfield Clemson University
Why does this course exist?
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Software is becoming more and more
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important
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complex Software is everywhere, at multiple levels: System, application, scientific, embedded, ubiquitous, web, AI, … We still do not know how to do it Techniques that we have been using for 60 years are inadequate Software engineering is an attempt to solve this problem Expect several generations for new habits/principles/procedures to be
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discovered
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transmitted (education)
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Adopted (replacing old habits)
The Software Crisis
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Standish Group (1995) studied S/W projects:
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16% successful (fully functional, on-time, and on-budget)
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53% challenged (reduced functionality, late, over-budget)
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31% failed (cancelled) More recent data (2006) suggests an improvement: 35%, 46%, and 19%
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Famous Bugs
1997: Mars Pathfinder
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three tasks: low-priority (weather data), medium-priority (communications), high-priority (information bus)
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priority inversion: Med interrupted Low before High could execute watchdog timer repeatedly rebooted system because High had not executed in time on-board debugging fixed the problem http://www.ece.cmu.edu/~raj/mars.html
1999: Mars Climate Orbiter
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Smashed into planet because units were not converted from English to metric
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$125 million spacecraft lost 2004: Mars rover Spirit
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Just after launch (June 2003), bug found in S/W, new version uploaded
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This caused side-effect, so another version uploaded
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After a few days, rover went into infinite reboot
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Longest trial for file system testing was 9 days 2004: Air traffic controller in Southern California
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Microsoft server timed to shut down automatically every 49.7 days to prevent data overload (2 32 milliseconds)
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Technicians normally reboot system every 30 days to avoid this One technician forgot
system shut down on its own 800 planes were left in the air without contact; 5 near misses 2005: Toyota Prius
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Bug caused gasoline engine to stall, often on highway 1995: Denver airport automated baggage system software
Another glitch
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"Last year in South Africa an anti-aircraft had a 'software glitch' during a training exercise," he says. "It was supposed to fire upwards into the sky, instead it lowered and it fired in a circle and killed nine soldiers, all because of a software glitch." http://www.cnn.com/2009/WORLD/america s/07/23/wus.warfare.remote.uav/index.html
S/W in automobiles
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Average automobile has
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70 to 100 microprocessor-based electronic control units (ECUs), running
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100 million lines of software code Control software logic analyzes vehicle load, engine operations, battery parameters, temperatures, ...
Software development is the single most important consideration in new product development engineering 35-40% of the cost of a car is software and electronics (13-15% of that cost is software development) 50% of car warranty costs are related to electronics and embedded software Bugs:
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2005: Toyota recalled >160000 Prius hybrids due to S/W problem
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May 2008: Chrysler recalled >20000 Jeep Commanders b/c bug in automatic transmission S/W
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June 2008: Volkswagen recalled ~4000 Passats and Tiguans for bug in engine control-module S/W
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November 2008: GM recalled >12000 Cadillacs that toggled air bag enable/disable bit
from Robert N. Charette, This Car Runs on Code, IEEE Spectrum, Feb. 2009
What is Software Engineering?
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The IEEE Computer Society defines software engineering as:
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(1) The application of a systematic, disciplined, quantifiable approach to the development, operation, and maintenance of software; that is, the application of engineering to software.
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(2) The study of approaches as in (1) If you do not find this helpful, you are not alone A better definition: “S/W engineering is applying sound engineering principles to develop reliable, efficient, economic S/W” – Pressman
What is S/W engineering?
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S/W engineering is about managing complexity and
change complexity
– many different conflicting objectives, lack of modularity
change
– requirements updated when developers/clients get better understanding of application, staff turn-around is high, time b/w technological changes shorter than duration of project “The only constant is change” S/W engineering focuses on quality (foundation)
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involves
Process
managed – defines framework in which S/W is developed and
Methods Tools
– activities involved – support the work
What is S/W engineering?
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Modeling
– one of the basic methods of science
Problem solving
– lack of fundamental theory leads to empirical methods to find solutions
Knowledge acquisition
– knowledge acquisition is a non-linear process; addition of new piece of knowledge may invalidate all previous knowledge; all activities are interrelated
Rationale-driven
– assumptions change continually; must capture context in which each decision was made
Product and process
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Product
– end result
Process
– how to get there Often seen as dichotomy (either-or). Field has vascillated back and forth over the years between the two.
In truth, there is a duality. Both are true, both are important, need to keep them in balance [Margaret Davis]
Balance, balance, balance!
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If you learn nothing else, remember this: Balance
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Lone-ranger mentality has a tendency to reject discipline (distrust theory)
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Academia has a tendency to over-emphasize discipline (theory more important than practice) Common sense usually works Be wary of absolutes (in software) Even very good programmers can be trapped by adherence to rules rather than focusing on the end product
The Controversy
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The term S/W engineering originated in 1968 at a conference in Germany But is the term meaningful?
S/W is fundamentally different from traditional engineering disciplines
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Not bound by laws of physics
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Nearly anything can change (plans, people, funding, milestones requirements, designs, tests)
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Metrics have no atomic units and are highly subjective Software development is more akin to movie production
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Produces complex web of intellectual property
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Limited only by vision and creativity It is a blend of science and art Some prefer software development, or software economics
[Walter Royce, Successful Software Management Style: Steering and Balance, IEEE Software, 20(5):40-47, 2005 ]
Other differences
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Unlike traditional engineering, S/W is developed, not manufactured Most S/W is still custom-built, not component-based construction S/W does not ‘wear out’, but it does deteriorate
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H/W failure curve vs. S/W failure curve S/W projects cannot be managed as if they were manufacturing projects
S/W Engineering is Management
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S/W Engineering is about instilling discipline into the development process
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Will make you a better programmer (self-management) Is necessary for managing teams of programmers (especially large teams) S/W Engineering is a collection of
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management techniques wisdom and advice gained from past projects (successes and failures)
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abstractions to mediate between low-level code and high-level human language
What, A Management Course?
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No, you will not be able to manage a large S/W project with hundreds of people by the end of this course Management skills take years to develop But, if we are successful, you will
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Be better able to manage your own code development
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Be equipped to work in (and perhaps lead) a small team of programmers
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Be alert to the struggles and issues faced by software managers
The Purpose of this Course
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Encounter the concepts / terms / methods of S/W Engineering
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Some of these are useful
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Even those that are not: You should be familiar with them, because you will encounter them
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Almost all are subject to change / disagreements Understanding the historical context and key players is important Gain practical experience
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Only way to master a craft is to do it – “Learning by doing”
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(Imagine a painting class without paint) Apply concepts as needed Non linear learning (“just in time learning”): Many concepts will not be taught until after you need them Develop proficiency with some additional tools
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C++, VC++, CVS, … Learn to learn
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Field is constantly changing
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Habit and ability to continue learning is essential to success
Course Mechanics
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Entire class will work on one project. Class will be divided into groups:
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groups will be self-directed, defining own milestones and tracking progress
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Weekly progress updates and goals (in class)
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Each group will present progress, issues
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Other groups will offer suggestions
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Code will be inspected, reviewed Individually,
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Attendance expected
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Individual project provides chance to develop individual programming skills
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Weekly written assignments Final exam will cover primarily “textbook” knowledge
Certification
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IEEE Computer Society offers two levels of software certification
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CSDA Certified Software Development Associate (introduced in 2008 for those at an entry level) http://www.computer.org/csda
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CSDP Certified Software Development Professional (introduced in 2002 for midcareer software development practitioners) http://www.computer.org/csdp Both comply with the ISO/IEC 24773 standard
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ISO/IEC 24773:2008 is called Software Engineering –Certification of Software Engineering Professionals –Comparison Framework
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uses the IEEE Computer Society’s Guide to the Software Engineering Body of Knowledge (SWEBOK) as its description of the profession
SWEBOK
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Guide to the Software Engineering Body of Knowledge (SWEBOK) is “the benchmark for defining and comparing certifications in software engineering,” – Jim Moore, 2008 chair of the IEEE Computer Society’s Professional Practices Committee, the group that oversees the certification programs.
http://www.swebok.org/
S/W Engineer
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A good software engineer
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knows how to identify requirements can properly categorize project risk can accurately estimate