ECE 417/617: Elements of Software Engineering

1
Introduction
ECE 417/617Elements of Software Engineering
Stan Birchfield Clemson University
2
Why does this course exist?

• Software is becoming more and more
• important
• 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
• discovered
• transmitted (education)
• Adopted (replacing old habits)

3
The Software Crisis

• Standish Group (1995) studied S/W projects
• 16 successful (fully functional, on-time, and
  on-budget)
• 53 challenged (reduced functionality, late,
  over-budget)
• 31 failed (cancelled)
• More recent data (2006) suggests an improvement
  35, 46, and 19

4
Famous Bugs

• 1997 Mars Pathfinder
• three tasks low-priority (weather data),
  medium-priority (communications), high-priority
  (information bus)
• 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
• Smashed into planet because units were not
  converted from English to metric
• 125 million spacecraft lost
• 2004 Mars rover Spirit
• Just after launch (June 2003), bug found in S/W,
  new version uploaded
• This caused side-effect, so another version
  uploaded
• After a few days, rover went into infinite reboot
• Longest trial for file system testing was 9 days
• 2004 Air traffic controller in Southern
  California
• Microsoft server timed to shut down automatically
  every 49.7 days to prevent data overload (232
  milliseconds)
• 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

5
Another glitch

• "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/americas/07/23/wus.w
  arfare.remote.uav/index.html

6
S/W in automobiles

• Average automobile has
• 70 to 100 microprocessor-based electronic control
  units (ECUs), running
• 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
• 2005 Toyota recalled gt160000 Prius hybrids due
  to S/W problem
• May 2008 Chrysler recalled gt20000 Jeep
  Commanders b/c bug in automatic transmission S/W
• June 2008 Volkswagen recalled 4000 Passats and
  Tiguans for bug in engine-control-module S/W
• November 2008 GM recalled gt12000 Cadillacs that
  toggled air bag enable/disable bit

from Robert N. Charette, This Car Runs on Code,
IEEE Spectrum, Feb. 2009
7
What is Software Engineering?

• The IEEE Computer Society defines software
  engineering as
• (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.
• (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

8
What is S/W engineering?

• 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
  projectThe only constant is change
• S/W engineering
• focuses on quality (foundation)
• involves
• Process defines framework in which S/W is
  developed and managed
• Methods activities involved
• Tools support the work

9
What is S/W engineering?

• 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

10
Product and process

• 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

11
Balance, balance, balance!

• If you learn nothing else, remember this
  Balance
• Lone-ranger mentality has a tendency to reject
  discipline (distrust theory)
• 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

12
The Controversy

• 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
• Not bound by laws of physics
• Nearly anything can change (plans, people,
  funding, milestones requirements, designs, tests)
• Metrics have no atomic units and are highly
  subjective
• Software development is more akin to movie
  production
• Produces complex web of intellectual property
• 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
13
Other differences

• 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
• H/W failure curve vs. S/W failure curve
• S/W projects cannot be managed as if they were
  manufacturing projects

14
S/W Engineering is Management

• S/W Engineering is about instilling discipline
  into the development process
• 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
• management techniques
• wisdom and advice gained from past projects
  (successes and failures)
• abstractions to mediate between low-level code
  and high-level human language

15
What, A Management Course?

• 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
• Be better able to manage your own code
  development
• Be equipped to work in (and perhaps lead) a small
  team of programmers
• Be alert to the struggles and issues faced by
  software managers

16
The Purpose of this Course

• Encounter the concepts / terms / methods of S/W
  Engineering
• Some of these are useful
• Even those that are not You should be familiar
  with them, because you will encounter them
• Almost all are subject to change / disagreements
• Understanding the historical context and key
  players is important
• Gain practical experience
• Only way to master a craft is to do it
  Learning by doing
• (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
• C, VC, CVS,
• Learn to learn
• Field is constantly changing
• Habit and ability to continue learning is
  essential to success

17
Course Mechanics

• Entire class will work on one project. Class
  will be divided into groups
• groups will be self-directed, defining own
  milestones and tracking progress
• Weekly progress updates and goals (in class)
• Each group will present progress, issues
• Other groups will offer suggestions
• Code will be inspected, reviewed
• Individually,
• Attendance expected
• Individual project provides chance to develop
  individual programming skills
• Weekly written assignments
• Final exam will cover primarily textbook
  knowledge

18
Certification

• IEEE Computer Society offers two levels of
  software certification
• CSDA Certified Software Development Associate
  (introduced in 2008 for those at an entry
  level)http//www.computer.org/csda
• CSDP Certified Software Development Professional
  (introduced in 2002 for midcareer software
  development practitioners) http//www.computer.or
  g/csdp
• Both comply with the ISO/IEC 24773 standard
• ISO/IEC 247732008 is calledSoftware
  EngineeringCertification of Software Engineering
  ProfessionalsComparison Framework
• uses the IEEE Computer Societys Guide to the
  Software Engineering Body of Knowledge (SWEBOK)
  as its description of the profession

19
SWEBOK

• 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 Societys Professional Practices
  Committee, the group that oversees the
  certification programs.
• http//www.swebok.org/

20
S/W Engineer

• A good software engineer
• knows how to identify requirements
• can properly categorize project risk
• can accurately estimate
• These skills are critical to providing customers
  with the correct product, on time, within
  budget. Susan K. (Kathy) Land