Transcript Document 7707309

Course Notes Set 1:
Introduction to
Software Engineering
Computer Science and Software Engineering
Auburn University
Auburn University
Computer Science and Software Engineering
COMP 6710 Course Notes Slide 1-0
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.
Auburn University
Computer Science and Software Engineering
COMP 6710 Course Notes Slide 1-1
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!
Auburn University
Computer Science and Software Engineering
COMP 6710 Course Notes Slide 1-2
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
Auburn University
Computer Science and Software Engineering
COMP 6710 Course Notes Slide 1-3
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].
Auburn University
Computer Science and Software Engineering
COMP 6710 Course Notes Slide 1-4
Software Death
[Adapted from Figure 1.2, Pressman5E]
Auburn University
Computer Science and Software Engineering
COMP 6710 Course Notes Slide 1-5
Software Has Changed
Then:
Now:
• Ran on single processor,
usually a mainframe
• Input was linear, sequential
• Output was alphanumeric
• System design dominated
by
• 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:
– Transform systems
– Transaction systems
–
–
–
–
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.
Auburn University
Computer Science and Software Engineering
COMP 6710 Course Notes Slide 1-6
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.
Auburn University
Computer Science and Software Engineering
COMP 6710 Course Notes Slide 1-7
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.
Auburn University
Computer Science and Software Engineering
COMP 6710 Course Notes Slide 1-8
… 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
Auburn University
Computer Science and Software Engineering
COMP 6710 Course Notes Slide 1-9
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]
Auburn University
Computer Science and Software Engineering
COMP 6710 Course Notes Slide 1-10
What is Software Engineering?
design
coding
CASE
maintenance
KLOC
structured analysis
software quality assurance
testing
project management
dataflow diagrams
requirements
metrics
configuration management
structure charts
Auburn University
Computer Science and Software Engineering
COMP 6710 Course Notes Slide 1-11
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]
tools
methods
process
a focus on quality
[Adapted from Pressman 5th Ed]
Auburn University
Computer Science and Software Engineering
COMP 6710 Course Notes Slide 1-12
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.
Auburn University
Computer Science and Software Engineering
COMP 6710 Course Notes Slide 1-13
Principles
• Abstraction
– Primary tool for managing complexity
– View a system in terms of layers or a
hierarchy or abstraction
Auburn University
Computer Science and Software Engineering
COMP 6710 Course Notes Slide 1-14
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)
Auburn University
Computer Science and Software Engineering
COMP 6710 Course Notes Slide 1-15
Principles
• Prototyping
– Help identify requirements
– Explore feasibility
– Simulate functions to be implemented
in hardware
Auburn University
Computer Science and Software Engineering
COMP 6710 Course Notes Slide 1-16
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)
Auburn University
Computer Science and Software Engineering
COMP 6710 Course Notes Slide 1-17
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
Auburn University
Computer Science and Software Engineering
COMP 6710 Course Notes Slide 1-18
Principles
• Measurement
– Quantification of attributes of product
and process
– Critical for assessment and
improvement
Auburn University
Computer Science and Software Engineering
COMP 6710 Course Notes Slide 1-19
Principles
• Tools and Environments
– Automated Software Engineering
– Vertical v. Horizontal tools
– Critical issues include
• Integration
• repositories
Auburn University
Computer Science and Software Engineering
COMP 6710 Course Notes Slide 1-20
Principles
• Software Process
– The organization and discipline of the
activities of developing software
– Process diversity needed
Auburn University
Computer Science and Software Engineering
COMP 6710 Course Notes Slide 1-21