Quality Assurance in SE lecture week 08 .ppt

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Lecture 11: Chapter 14
 Quality Concepts
Slide Set to accompany
Software Engineering: A Practitioner’s Approach, 7/e
by Roger S. Pressman
Slides copyright © 1996, 2001, 2005, 2009 by Roger S. Pressman
For non-profit educational use only
May be reproduced ONLY for student use at the university level when used in conjunction
with Software Engineering: A Practitioner's Approach, 7/e. Any other reproduction or use is
prohibited without the express written permission of the author.
All copyright information MUST appear if these slides are posted on a website for student
use.

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Software Quality
 In 2005, ComputerWorld [Hil05] lamented that
 “bad software plagues nearly every organization that uses
computers, causing lost work hours during computer downtime,
lost or corrupted data, missed sales opportunities, high IT support
and maintenance costs, and low customer satisfaction.
 A year later, InfoWorld [Fos06] wrote about the
 “the sorry state of software quality” reporting that the quality
problem had not gotten any better.
 Today, software quality remains an issue, but who is to blame?
 Customers blame developers, arguing that sloppy practices lead to
low-quality software.
 Developers blame customers (and other stakeholders), arguing that
irrational delivery dates and a continuing stream of changes force
them to deliver software before it has been fully validated.

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Quality
 The American Heritage Dictionary defines
quality as
 “a characteristic or attribute of something.”
 For software, two kinds of quality may be
encountered:
 Quality of design encompasses requirements,
specifications, and the design of the system.
 Quality of conformance is an issue focused primarily
on implementation.
 User satisfaction = compliant product + good quality
+ delivery within budget and schedule

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Software Quality
 Software quality can be defined as:
 An effective software process applied in a manner that
creates a useful product that provides measurable value for
those who produce it and those who use it.
 This definition has been adapted from [Bes04] and
replaces a more manufacturing-oriented view
presented in earlier editions of this book.

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Effective Software Process
 An effective software process establishes the infrastructure
that supports any effort at building a high quality
software product.
 The management aspects of process create the checks
and balances that help avoid project chaos—a key
contributor to poor quality.
 Software engineering practices allow the developer to
analyze the problem and design a solid solution—both
critical to building high quality software.
 Finally, umbrella activities such as change management
and technical reviews have as much to do with quality
as any other part of software engineering practice.

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Useful Product
 A useful product delivers the content, functions,
and features that the end-user desires
 But as important, it delivers these assets in a
reliable, error free way.
 A useful product always satisfies those
requirements that have been explicitly stated by
stakeholders.
 In addition, it satisfies a set of implicit
requirements (e.g., ease of use) that are
expected of all high quality software.

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Adding Value
 By adding value for both the producer and user of a software
product, high quality software provides benefits for the
software organization and the end-user community.
 The software organization gains added value because
high quality software requires less maintenance effort,
fewer bug fixes, and reduced customer support.
 The user community gains added value because the
application provides a useful capability in a way that
expedites some business process.
 The end result is:
 (1) greater software product revenue,
 (2) better profitability when an application supports a
business process, and/or
 (3) improved availability of information that is crucial for
the business.

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Quality Dimensions
 David Garvin [Gar87]:
 Performance Quality. Does the software deliver all
content, functions, and features that are specified as part of
the requirements model in a way that provides value to the
end-user?
 Feature quality. Does the software provide features that
surprise and delight first-time end-users?
 Reliability. Does the software deliver all features and
capability without failure? Is it available when it is needed?
Does it deliver functionality that is error free?
 Conformance. Does the software conform to local and
external software standards that are relevant to the
application? Does it conform to de facto design and coding
conventions? For example, does the user interface conform
to accepted design rules for menu selection or data input?

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Quality Dimensions
 Durability. Can the software be maintained (changed) or
corrected (debugged) without the inadvertent generation of
unintended side effects? Will changes cause the error rate
or reliability to degrade with time?
 Serviceability. Can the software be maintained (changed)
or corrected (debugged) in an acceptably short time period.
Can support staff acquire all information they need to
make changes or correct defects?
 Aesthetics. Most of us would agree that an aesthetic entity
has a certain elegance, a unique flow, and an obvious
“presence” that are hard to quantify but evident
nonetheless.
 Perception. In some situations, you have a set of prejudices
that will influence your perception of quality.

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Other Views
 McCall’s Quality Factors (SEPA, Section
14.2.2)
 ISO 9126 Quality Factors (SEPA, Section
14.2.3)
 Targeted Factors (SEPA, Section 14.2.4)

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The Software Quality Dilemma
 If you produce a software system that has terrible
quality, you lose because no one will want to buy it.
 If on the other hand you spend infinite time, extremely
large effort, and huge sums of money to build the
absolutely perfect piece of software, then it's going to
take so long to complete and it will be so expensive to
produce that you'll be out of business anyway.
 Either you missed the market window, or you simply
exhausted all your resources.
 So people in industry try to get to that magical middle
ground where the product is good enough not to be
rejected right away, such as during evaluation, but also
not the object of so much perfectionism and so much
work that it would take too long or cost too much to
complete. [Ven03]

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“Good Enough” Software
 Good enough software delivers high quality functions and
features that end-users desire, but at the same time it delivers
other more obscure or specialized functions and features that
contain known bugs.
 Arguments against “good enough.”
 It is true that “good enough” may work in some application
domains and for a few major software companies. After all, if a
company has a large marketing budget and can convince enough
people to buy version 1.0, it has succeeded in locking them in.
 If you work for a small company be wary of this philosophy. If you
deliver a “good enough” (buggy) product, you risk permanent
damage to your company’s reputation.
 You may never get a chance to deliver version 2.0 because bad
buzz may cause your sales to plummet and your company to fold.
 If you work in certain application domains (e.g., real time
embedded software, application software) that is integrated with
hardware can be negligent and open your company to expensive
litigation.

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Cost of Quality
 Prevention costs include
 quality planning
 formal technical reviews
 test equipment
 Training
 Internal failure costs include
 rework
 repair
 failure mode analysis
 External failure costs are
 complaint resolution
 product return and replacement
 help line support
 warranty work

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Cost
 The relative costs to find and repair an error or defect
increase dramatically as we go from prevention to
detection to internal failure to external failure costs.

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Quality and Risk
 “People bet their jobs, their comforts, their safety, their
entertainment, their decisions, and their very lives on
computer software. It better be right.” SEPA, Chapter 1
 Example:
 Throughout the month of November, 2000 at a hospital in
Panama, 28 patients received massive overdoses of gamma rays
during treatment for a variety of cancers. In the months that
followed, five of these patients died from radiation poisoning and
15 others developed serious complications. What caused this
tragedy? A software package, developed by a U.S. company, was
modified by hospital technicians to compute modified doses of
radiation for each patient.

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Negligence and Liability
 The story is all too common. A governmental or
corporate entity hires a major software developer or
consulting company to analyze requirements and then
design and construct a software-based “system” to
support some major activity.
 The system might support a major corporate function (e.g.,
pension management) or some governmental function (e.g.,
healthcare administration or homeland security).
 Work begins with the best of intentions on both sides,
but by the time the system is delivered, things have gone
bad.
 The system is late, fails to deliver desired features and
functions, is error-prone, and does not meet with
customer approval.
 Litigation ensues.

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Quality and Security
 Gary McGraw comments [Wil05]:
 “Software security relates entirely and completely to
quality. You must think about security, reliability,
availability, dependability—at the beginning, in the
design, architecture, test, and coding phases, all through
the software life cycle [process]. Even people aware of
the software security problem have focused on late life-
cycle stuff. The earlier you find the software problem,
the better. And there are two kinds of software
problems. One is bugs, which are implementation
problems. The other is software flaws—architectural
problems in the design. People pay too much attention to
bugs and not enough on flaws.”

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Achieving Software Quality
 Critical success factors:
 Software Engineering Methods
 Project Management Techniques
 Quality Control
 Quality Assurance

Quality Assurance in SE lecture week 08 .ppt

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