Software Engineering (Software Quality Assurance)

Software Engineering
(CSI 321)
Software Quality Assurance
1

Introduction
 Software Quality Assurance (SQA) is an umbrella activity that is applied
throughout the software process.
 SQA encompasses-
1) A software quality assurance process
2) Specific quality assurance and quality control tasks ( including formal
technical reviews and a multi-tier testing strategy)
3) Effective software engineering practice (methods and tools)
4) Control of all software work products and the changes made to them
5) A procedure to ensure compliance with software development standards
6) Measurement and reporting mechanisms
2

Quality Concepts
• Software engineers strive to control the
– process applied
– resources expended
– end product quality attributes
3

What is Quality ?
• Refers to measurable characteristics.
• For software, two kinds of quality may be encountered:
 Quality of design: refers to characteristics that designers specify for the
end product to be constructed. Quality of design encompasses
requirements, specifications, and the design of the system.
 Quality of conformance: is the degree to which design
specifications are followed during developing the product. Quality of
conformance is an issue focused primarily on implementation.
• Crucial is customer satisfaction (and quality is only a part of it):
 User satisfaction = compliant product + good quality + delivery within budget
and schedule
• At the bottom line ==> Quality is important, but if the user isn’t satisfied,
nothing else really matters!
4

Quality Control (QC)
• QC is defined as the processes and methods used to monitor
work and observe whether requirements are met. It focuses
on reviews and removal of defects before shipment of
products.
• QC involves series of inspections, reviews, and tests used
throughout the software process to ensure each work
product meets the requirements placed upon it.
• QC includes a feedback loop to the process that created the
work product.
5

Quality Control (QC)
• A key concept of quality control is that all work
products have defined, measurable specifications to
which we may compare the output of each process.
Feedback loop is essential to minimize the defects
produced.
• QC is the operational techniques and activities used
to fulfill and verify requirements of quality.
• Quality Control is a product-oriented activity.
6

Quality Assurance
• QA consists of a set of auditing and reporting
functions that assess the effectiveness, correctness,
and completeness of QC activities.
• The goal of QA is to provide management with the
data necessary to be informed about product quality,
thereby gaining insight and confidence that product
quality is meeting its goals.
7

Quality Assurance
• QA is the process of defining how software quality can be
achieved and how the development organization knows that
the software has the required level of quality.
• QA is a planned and systematic pattern of all actions
necessary to provide adequate confidence that an item or
product conforms to established technical requirements.
• QA is an effective approach for producing high quality
product.
• QA is a process-oriented activity and it is oriented to bug-
prevention.
8

Cost of Quality
• Quality costs may be divided into costs associated with
prevention, appraisal, and failure
1) Prevention costs include quality planning, formal
technical reviews, test equipment, training.
2) Appraisal costs include activities to gain insight into
product condition
3) Failure costs are those that would disappear if no defects
appeared before shipping a product to customer.
– Internal
– External
9

Failure Costs
• Failure Costs may be subdivided into two categories-
a) Internal failure costs are incurred when we detect a defect in
our product prior to shipment.
–rework, repair, failure mode analysis
b) External failure costs are associated with defects found after
the product has been shipped to the customer.
–complaint resolution, product return and replacement, help
line support, warranty work
10

Cost of Correcting Defects
• Relative costs to find and repair a defect increase
dramatically:
– From prevention to detection
– From internal vs. external
• IBM example:
– Prevention = ~$90/defect
– Field fix = ~$25,000/defect
11

Relative cost of correcting an errors
12

Software Quality
• Conformance to explicitly stated functional and
performance requirements, explicitly documented
development standards, and implicit characteristics
that are expected of all professionally developed
software.
13

Software Quality Assurance(SQA)
Software quality assurance [IEEE]:
1. A planned and systematic pattern of all actions
necessary to provide adequate confidence that an
item or product conforms to established technical
requirements.
2. A set of activities designed to evaluate the process
by which the products are developed or
manufactured.
14

Software Quality Assurance(SQA)
 Three important points for software quality:
1) Software requirements are the foundation from which quality
is measured. Lack of conformance to requirements is lack of
quality.
2) Specified standards define a set of development criteria that
guide the manner in which software is engineered.
3) Software must conform to explicit requirements as well as its
implicit requirements (ease of use, maintainability, reliability,
etc.).
15

What is the role of an SQA group?
1) Prepare SQA plan for the project.
2) Participate in the development of the project's software process
description.
3) Review software engineering activities to verify compliance with
the defined software process.
4) Audit designated software work products to verify compliance
with those defined as part of the software process.
5) Ensure that any deviations in software or work products are
documented and handled according to a documented procedure.
6) Record any evidence of noncompliance and reports them to senior
management.
16

Software Reviews
• Software reviews are like “filters” in the software
process workflow.
• Software reviews are applied at various points during
software engineering and serve to uncover errors
and defects that can then be removed.
• Software reviews “purify” the software engineering
activities.
17

Software Reviews
• Purpose is to find defects (errors) before they are
passed on to another software engineering activity
or released to the customer.
• Software engineers (and others) conduct formal
technical reviews (FTR) for software engineers.
• Using formal technical reviews is an effective means
for improving software quality.
18

What Are Reviews?
• A meeting conducted by technical people for
technical people
• A technical assessment of a work product created
during the software engineering process
• A software quality assurance mechanism
• A training ground
19

What Reviews Are Not …
• A project summary or progress assessment
• A meeting intended solely to impart information
• A mechanism for political or personal reprisal!
20

Defect Amplification Models
• Defect amplification models can be used to illustrate
the generation and detection of errors during the
preliminary design, detail design, and coding steps of
a software engineering process.
• They are simple mathematical models for describing
how defects are propagated through the various
steps in the software development process.
21

Formal Technical Review(FTR)
• The primary objective of an FTR is to find errors
before they are passed on to another software
engineering activity or released to the end-user.
• A formal technical review (FTR) is the most effective
filter from a quality assurance standpoint.
• Conducted by software engineers (and others) for
software engineers, the FTR is an effective means for
uncovering errors and improving software quality.
22

Formal Technical Review(FTR)
 Objectives of Formal Technical Review (FTR):
1) To uncover errors in function, logic, or implementation
2) To verify that the software under review meets its
requirements
3) To ensure that the software has been represented according
to predefined standards
4) To achieve software that is developed in a uniform manner
5) To make projects more manageable
23

Formal Technical Review: The Roles
• Presenter (designer/producer)
• Coordinator (not a person who hires/fires)
• Recorder
– records events of meeting
– builds paper trail
• Reviewers
– maintenance person
– standards bearer
– User/customer representative or, play the role of
user/customer
– designers etc.
24

Formal Technical Reviews-1
• Typically involves 3 to 5 people (including reviewers)
• Advance preparation (no more than 2 hours per
person) required
• Duration of review meeting should be less than 2
hours
• Focus of review is on a discrete work product
• Review leader organizes the review meeting at the
producer's request.
25

Formal Technical Reviews - 2
• Reviewers ask questions that enable the producer to
discover his or her own error (the product is under
review, not the producer)
• Producer of the work product walks the reviewers
through the product
• Recorder writes down any significant issues raised
during the review
• Reviewers decide to accept or reject the work
product and whether to require additional reviews of
product or not.
26

Why do we conduct reviews?
• To improve quality.
• Catches 80% of all errors if done properly.
• Catches both coding errors and design errors.
• Enforce the spirit of any organization standards.
27

Formality and Timing
• Formal review presentations
– resemble conference presentations.
• Informal presentations
– less detailed, but equally correct.
• Early
– tend to be informal
– may not have enough information
• Later
– tend to be more formal
– Feedback may come too late to avoid rework
28

Formality and Timing
• Analysis is complete
• Design is complete
• After first compilation
• After first test run
• After all test runs
• Any time you complete an activity that produce a
complete work product
29

Review Guidelines
• Keep it short (< 1 hour).
• Don’t schedule two in a row.
• Don’t review product fragments.
• Use standards to avoid style disagreements.
• Let the coordinator run the meeting and maintain
order.
30

Formal Approaches to SQA
1) Proof of correctness
2) Statistical SQA
3) Cleanroom process combines items 1 & 2.
31

Statistical Software Quality Assurance
 Statistical Software Quality Assurance helps to improve the
quality of the product and software process itself.
 Steps to perform Statistical SQA:
1) Information about software defects is collected and
categorized
2) Each defect is traced back to its underlying cause
3) Using the Pareto principle (80% of the defects can be
traced to 20% of all possible causes), isolate the "vital
few" defect causes
4) Move to correct the problems that caused the defects
32

33
Six Sigma for Software Engineering
 Six Sigma is the most widely used strategy for statistical quality
assurance in industry.
• The term “six sigma” is derived from six standard deviations—3.4
instances (defects) per million occurrences—implying an extremely
high quality standard.
• The Six Sigma methodology defines three core steps:
1) Define customer requirements and deliverables and project
goals via well-defined methods of customer communication
2) Measure the existing process and its output to determine
current quality performance (collect defect metrics)
3) Analyze defect metrics and determine the vital few causes.

Six Sigma for Software Engineering
• Six Sigma suggests two additional steps to improve
an existing software process:
– Improve the process by eliminating the root causes of
defects.
– Control the process to ensure that future work does not
reintroduce the causes of defects.
34

Software Reliability
• Software reliability is defined as “the probability of
failure-free operation of a computer program in a
specified environment for a specified time”
• Can be measured directly and estimated using
historical and developmental data (unlike many
other software quality factors)
• Software reliability problems can almost always be
traced back to defects in design or implementation.
35

Reliability Metrics
Measures of Reliability:
• A simple measure of reliability is mean-time-between-failure
(MTBF), where
• MTBF = MTTF + MTTR
• MTTF = mean time to failure
• MTTR = mean time to repair
• Software Availability is the probability that a program is
operating according to requirements at a given point in time
and is defined as :
Availability = [MTTF/ (MTTF+MTTR)] x 100%
• Reliability = MTTF/ (1 + MTTF) X 100%
36

Software Safety
• Safety may be defined as "freedom from those conditions
that can cause death, injury, occupational ill-ness, or damage
to or loss of equipment or property." But safety is a relative
concept. Nothing is absolutely safe under all conditions.
• Software safety issues become important when computers
are used to control real-time, safety-critical processes.
• Software safety is a SQA activity that focuses on identification
and assessment of potential hazards that may affect software
negatively and cause an entire system to fail.
• Early identification of software hazards allows developers to
specify design features that can eliminate or at least control
the impact of potential hazards.
37

Software Reliability vs. Software Safety
• Both are closely related to each other.
• Subtle difference:
– Software reliability uses statistical analysis to
determine the likelihood that a software failure
will occur without regard to consequences of
failures.
– Software safety examines the ways in which
failures result in conditions that can lead to
mishap.
38

Quality Standards
 ISO-9126 Quality Framework:
• The most influential one in the software engineering
community today.
• Provides a hierarchical framework for quality
definition, organized into quality characteristics and
sub-characteristics
• Six top-level quality characteristics, each associated
with its own exclusive(non-overlapping) sub-
characteristics
39

Quality Standards
 ISO-9126 quality characteristics:
1) Functionality
2) Reliability
3) Usability
4) Efficiency
5) Maintainability
6) Portability
40

Other Quality Frameworks
 Adaptation of ISO-9126:
Customized for companies
– e.g. IBM’s CUPRIMDSO( Capability, Usability, Performance,
Reliability, Installation, Maintenance, Documentation, Service,
Overall customer satisfaction)
Adapted to application domains
– Reliability, usability, security for Web
 Other quality frameworks/mega-models
– SEI/CMMI: process focus/levels
– McCall: factors, criteria
– Basili: GQM (goal-question-metric)
– Dromey: component reflects Q-attributes
41

SQA Plan
The SQA Plan provides a road map for instituting software quality
assurance. Developed by the SQA group, the plan serves as a
template for SQA activities that are instituted for each software
project.
• Management section
– describes the place of SQA in the structure of the organization
• Documentation section
– describes each work product produced as part of the software
process
• Standards, practices, and conventions section
– lists all applicable standards/practices applied during the
software process and any metrics to be collected as part of the
software engineering work
42

SQA Plan
• Reviews and audits section
– provides an overview of the approach used in the reviews and audits
to be conducted during the project
• Test section
– references the test plan and procedure document and defines test
record keeping requirements
• Problem reporting and corrective action section
– defines procedures for reporting, tracking, and resolving errors or
defects, identifies organizational responsibilities for these activities
• Other
– tools, SQA methods, change control, record keeping, training, and risk
management
43

Software Engineering (Software Quality Assurance)

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Software Engineering (Software Quality Assurance)