1. COMP 6710 Course Notes Slide 1-1
Auburn University
Computer Science and Software Engineering
Course Notes Set 1:
Introduction to
Software Engineering
Computer Science and Software Engineering
Auburn University
2. COMP 6710 Course Notes Slide 1-2
Auburn University
Computer Science and Software Engineering
Desirable Attributes of Software
• Maintainability
– It should be possible to evolve software to
meet the changing needs of customers.
• Dependability
– Software dependability includes a variety
of things such as reliability, security and
safety. Dependable software should not
cause physical or economic damage in the
event of a system failure.
3. COMP 6710 Course Notes Slide 1-3
Auburn University
Computer Science and Software Engineering
Desirable Attributes of Software
• Efficiency
– Software should not waste system
resources such as memory and processor
cycles.
• Usability
– Software should have an appropriate user
interface and adequate documentation.
• Etc., etc.
Achieving these qualities in software is hard to do!
4. COMP 6710 Course Notes Slide 1-4
Auburn University
Computer Science and Software Engineering
No Silver Bullet
But as we look to the horizon of a decade hence, we see no silver
bullet. There is no single development, either in technology or
management technique, which by itself promises even one order
of magnitude improvement in productivity, in reliability, in simplicity.
Not only are there no silver bullets in view, the very nature of software
makes it unlikely there will be any.
Frederick Brooks, The Mythical Man Month
5. COMP 6710 Course Notes Slide 1-5
Auburn University
Computer Science and Software Engineering
Software Characteristics
• Software is a crucial element of our society.
• Software is becoming ubiquitous and invisible.
• Software is both a product and a vehicle for delivering a
product.
• Software consists of programs, documents, and data.
• Software is developed or engineered, not
manufactured.
• Software is primarily custom-built, not assembled from
existing components.
• Software deteriorates, but doesn’t “wear out.”
• Software has a “chronic affliction” [Pressman 5th Ed].
6. COMP 6710 Course Notes Slide 1-6
Auburn University
Computer Science and Software Engineering
Software Death
idealized curve
change
actual curve
Failure
rate
Time
increased failure
rate due to side effects
[Adapted from Figure 1.2, Pressman5E]
7. COMP 6710 Course Notes Slide 1-7
Auburn University
Computer Science and Software Engineering
Software Has Changed
• Ran on single processor,
usually a mainframe
• Input was linear, sequential
• Output was alphanumeric
• System design dominated by
– Transform systems
– Transaction systems
• Delivered across a network;
distributed, multiple
processors; client-server.
• Input often from multiple
concurrent sources
• Output must meet demands
for sophisticated
visualization
• In addition to functional
requirements, must also
address:
– network control
– security
– UI issues
– data/object management
Demarco: We’ve solved the easy problems first. The ones that are left are the hard ones.
Then: Now:
8. COMP 6710 Course Notes Slide 1-8
Auburn University
Computer Science and Software Engineering
Major Agents of Change
• Compressed time-to-market, tight labor
market
• Hardware costs down, software costs up
• Powerful computing in small boxes
• Pervasive networking
• Ubiquity of object technology
• Expectation of sophisticated GUIs
• Inappropriateness of classic software
development process
Adapted from “Toward a Discipline of Software Engineering,” IEEE Software, Vol. 13, No. 6.
9. COMP 6710 Course Notes Slide 1-9
Auburn University
Computer Science and Software Engineering
Problems
• Many critical systems are controlled or influenced by
legacy software which is difficult or impossible to
maintain, not understandable, or irreplaceable.
• Little data exists on the process of developing software.
• Software quality is difficult to define and measure.
• Software doesn’t have spare parts.
• Software project managers are sometimes far removed
from software development.
• Software developers are sometimes unaware of
engineering approaches to developing software.
• Programming as an art versus programming as a
science.
• Many myths pervade the software development culture.
10. COMP 6710 Course Notes Slide 1-10
Auburn University
Computer Science and Software Engineering
… I would try to make some improvements in the
codes. Many codes or subroutines are more than
40 years old, and the guys who wrote them are
either in heaven or hell. Some codes are impossible
to refine because nobody knows what the original
programmer was trying to do. To figure it out, you
have to read the code in FORTRAN line by line, to
try to understand the underlying mathematics
picture – and these codes are hundreds of
thousands, even millions of line long. Once
someone found a bug in the code and removed it –
but then the code wouldn’t work. So they put the
bug back in, even though no one knew why the
program work that way.
(by a nuclear scientist)
- Page 113, My Country verse Me, Dr. Wen-ho Lee, Hyperion Pub., 2001
11. COMP 6710 Course Notes Slide 1-11
Auburn University
Computer Science and Software Engineering
Myths
• A general statement of objectives is enough to get
going. Fill in the details later.
• Project requirements continually change, but change can
be easily accommodated because software is flexible.
• Once a program is developed, tested, and delivered, the
developer’s job is done.
• Until a program is running, there is no way to assess its
quality.
• The only deliverable for a successful project is a working
program.
• We can always add more programmers if the project
gets behind.
• All programmers are created equal.
[Adapted from public domain SEI course notes by Carter and Conn]
12. COMP 6710 Course Notes Slide 1-12
Auburn University
Computer Science and Software Engineering
What is Software Engineering?
coding
testing
maintenance
design
structured analysis
dataflow diagrams
structure charts
software quality assurance
configuration management
project management
CASE
requirements
KLOC
metrics
13. COMP 6710 Course Notes Slide 1-13
Auburn University
Computer Science and Software Engineering
Software Engineering
• The establishment and use of sound engineering principles in
order to obtain economically software that is reliable and
works efficiently on real machines. [Bauer]
• The application of a systematic, disciplined, quantifiable
approach to the development, operation, and maintenance of
software; that is, the application of engineering to software.
[IEEE Standard 610.12-1990]
a focus on quality
process
methods
tools
[Adapted from Pressman 5th Ed]
14. COMP 6710 Course Notes Slide 1-14
Auburn University
Computer Science and Software Engineering
Principles of Software Engineering
• Abstraction
• Analysis and Design Methods and
Notations
• Prototyping
• Software Architecture
• Reuse
• Measurement
• Tools and Environments
• Software Process
Adapted from “Toward a Discipline of Software Engineering,” IEEE Software, Vol. 13, No. 6.
15. COMP 6710 Course Notes Slide 1-15
Auburn University
Computer Science and Software Engineering
Principles
• Abstraction
– Primary tool for managing complexity
– View a system in terms of layers or a
hierarchy or abstraction
16. COMP 6710 Course Notes Slide 1-16
Auburn University
Computer Science and Software Engineering
Principles
• Analysis and Design Methods and
Notations
– Notations
• A formal way of documenting and communicating
design decisions
• Issues: Cognitive aspects, readership skills, no
standards
– Methods
• A formal or semi-formal approach to building
models
• Allows for completeness and consistency checks
(ideally)
17. COMP 6710 Course Notes Slide 1-17
Auburn University
Computer Science and Software Engineering
Principles
• Prototyping
– Help identify requirements
– Explore feasibility
– Simulate functions to be implemented
in hardware
18. COMP 6710 Course Notes Slide 1-18
Auburn University
Computer Science and Software Engineering
Principles
• Software Architecture
– Specifies a system in terms of
architectural units and how they
relate
– Good architecture aids
implementation, testing, maintenance
– Becoming a sub-discipline (e.g.,
Garlan and Shaw)
19. COMP 6710 Course Notes Slide 1-19
Auburn University
Computer Science and Software Engineering
Principles
• Reuse
– Make use of commonalities among systems to
reuse requirements, designs, code, test scripts,
etc.
– Reusable components can be a business asset
– Barriers to reuse:
• Can be faster to build a small component from scratch
• May take extra time to build a reusable component
• Potential adopters may hesitate due to SQA concerns
• Liability issues in the event of failure or needed updates
• Program understanding issues
20. COMP 6710 Course Notes Slide 1-20
Auburn University
Computer Science and Software Engineering
Principles
• Measurement
– Quantification of attributes of product
and process
– Critical for assessment and
improvement
21. COMP 6710 Course Notes Slide 1-21
Auburn University
Computer Science and Software Engineering
Principles
• Tools and Environments
– Automated Software Engineering
– Vertical v. Horizontal tools
– Critical issues include
• Integration
• repositories
22. COMP 6710 Course Notes Slide 1-22
Auburn University
Computer Science and Software Engineering
Principles
• Software Process
– The organization and discipline of the
activities of developing software
– Process diversity needed