05_SQA_Overview.ppt

COMP 6710 Course Notes Slide 5-0
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Computer Science and Software Engineering
Course Notes Set 5:
Software Quality Assurance
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What is Software Quality?
• Simplistically, quality is an attribute of
software that implies the software
meets its specification
• This definition is too simple for ensuring
quality in software systems
– Software specifications are often incomplete
or ambiguous
– Some quality attributes are difficult to
specify
– Tension exists between some quality
attributes, e.g. efficiency vs. reliability

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Software Quality Attributes
• Safety
• Security
• Reliability
• Resilience
• Robustness
• Understandability
• Testability
• Adaptability
• Modularity
• Complexity
• Portability
• Usability
• Reusability
• Efficiency
• Learnability

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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
– Software requirements are the foundation from which
quality is measured.
• Lack of conformance to requirements is lack of quality.
– Specified standards define a set of development criteria
that guide the manner in which software is engineered.
• If the criteria are not met, lack of quality will almost surely
result.
– There is a set of implicit requirements that often goes
unmentioned.
• If software conforms to its explicit requirements but fails to
meet its implicit requirements, software quality is suspect.
[Adapted from Pressman 4th Ed]

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Software Quality Assurance
• To ensure quality in a software product, an organization must
have a three-prong approach to quality management:
– Organization-wide policies, procedures and standards must be
established.
– Project-specific policies, procedures and standards must be
tailored from the organization-wide templates.
– Quality must be controlled; that is, the organization must ensure
that the appropriate procedures are followed for each project
• Standards exist to help an organization draft an appropriate
software quality assurance plan.
– ISO 9000-3
– ANSI/IEEE standards
• External entities can be contracted to verify that an
organization is standard-compliant.

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A Software Quality Plan
ISO 9000
model
Organization
quality plan
Project A
quality plan
Project B
quality plan
Project C
quality plan
[Adapted from Sommerville 5th Ed]

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SQA Activities
• Applying technical methods
– To help the analyst achieve a high quality specification and a high quality design
• Conducting formal technical reviews
– A stylized meeting conducted by technical staff with the sole purpose of
uncovering quality problems
• Testing Software
– A series of test case design methods that help ensure effective error detection
• Enforcing standards
• Controlling change
– Applied during software development and maintenance
• Measurement
– Track software quality and asses the ability of methodological and procedural
changes to improve software quality
• Record keeping and reporting
– Provide procedures for the collection and dissemination of SQA information

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Advantages of SQA
• Software will have fewer latent defects,
resulting in reduced effort and time
spent during testing and maintenance
• Higher reliability will result in greater
customer satisfaction
• Maintenance costs can be reduced
• Overall life cycle cost of software is
reduced

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Disadvantages of SQA
• It is difficult to institute in small
organizations, where available
resources to perform necessary
activities are not available
• It represents cultural change - and
change is never easy
• It requires the expenditure of dollars
that would not otherwise be explicitly
budgeted to software engineering or
QA

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Quality Reviews
• The fundamental method of validating the quality of a
product or a process.
• Applied during and/or at the end of each life cycle phase
– Point out needed improvements in the product of a single
person or team
– Confirm those parts of a product in which improvement is
either not desired or not needed
– Achieve technical work of more uniform, or at least more
predictable, quality than what can be achieved without
reviews, in order to make technical work more
manageable
• Quality reviews can have different intents:
– review for defect removal
– review for progress assessment
– review for consistency and conformance

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Quality Reviews
Requirements
Analysis
Design
Code
Testing
Maintenance
1x
3-6x
10x
15-70x
40-1000x
Specification
Review
Design
Review
Code
Review
Test
Review
Customer
Feedback

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Cost Impact of Software
Defects
Errors Passed Through Percent Efficiency
Amplified Errors 1:X for error
Newly Generated Errors detection
Errors from
Previous
Steps
Errors
Passed to
Next Step

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Defect Amplification and
Removal
0
0 0%
10 6
4x1.5 0%
25 10
27x3 20%
25
Preliminary Design
Detailed Design
Code/Unit Testing
10
6
4
37
37
10
27
116
94
To integration
testing...

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Defect Amplification (cont’d)
94
0 50%
0 47
0 50%
0 24
0 50%
0
Integration Testing
Validation Testing
System Testing
94
94
0
94
47
47
47
24
24
24
0
0 12
Latent Errors

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Review Checklist for Systems
Engineering
• Are major functions defined in a bounded and
unambiguous fashion?
• Are interfaces between system elements defined?
• Are performance bounds established for the system as a
whole and for each element?
• Are design constraints established for each element?
• Has the best alternative been selected?
• Is the solution technologically feasible?
• Has a mechanism for system validation and verification
been established?
• Is there consistency among all system elements?
[Adapted from Behforooz and Hudson]

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Review Checklist for
Software Project Planning
• Is the software scope unambiguously defined and
bounded?
• Is terminology clear?
• Are resources adequate for the scope?
• Are resources readily available?
• Are tasks properly defined and sequenced?
• Is the basis for cost estimation reasonable? Has it been
developed using two different sources?
• Have historical productivity and quality data been used?
• Have differences in estimates been reconciled?
• Are pre-established budgets and deadlines realistic?
• Is the schedule consistent?

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Software Requirements
Analysis
• Is the information domain analysis complete,
consistent, and accurate?
• Is problem partitioning complete?
• Are external and internal interfaces properly defined?
• Are all requirements traceable to the system level?
• Is prototyping conducted for the customer?
• Is performance achievable with constraints imposed by
other system elements?
• Are requirements consistent with schedule, resources,
and budget?
• Are validation criteria complete?

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Software Design
(Preliminary Design Review)
• Are software requirements reflected in the
software architecture?
• Is effective modularity achieved? Are modules
functionally independent?
• Is program architecture factored?
• Are interfaces defined for modules and
external system elements?
• Is data structure consistent with software
requirements?
• Has maintainability been considered?

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Software Design
(Design Walkthrough)
• Does the algorithm accomplish the desired function?
• Is the algorithm logically correct?
• Is the interface consistent with architectural design?
• Is logical complexity reasonable?
• Have error handling and “antibugging” been specified?
• Is local data structure properly defined?
• Are structured programming constructs used throughout?
• Is design detail amenable to the implementation language?
• Which are used: operating system or language dependent
features?
• Is compound or inverse logic used?
• Has maintainability been considered?

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Review Checklist for Coding
• Is the design properly translated into code? (The
results of the procedural design should be available at
this review)
• Are there misspellings or typos?
• Has proper use of language conventions been made?
• Is there compliance with coding standards for language
style, comments, module prologue?
• Are incorrect or ambiguous comments present?
• Are typing and data declaration proper?
• Are physical constraints correct?
• Have all items on the design walkthrough checklist been
reapplied (as required)?

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Software Testing (Test Plan)
• Have major test phases been properly identified and
sequenced?
• Has traceability to validation criteria/requirements been
established as part of software requirements analysis?
• Are major functions demonstrated early?
• Is the test plan consistent with the overall project plan?
• Has a test schedule been explicitly defined?
• Are test resources and tools identified and available?
• Has a test recordkeeping mechanism been established?
• Have test drivers and stubs been identified, and has
work to develop them been scheduled?
• Has stress testing for software been specified?

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Software Testing
(Test Procedure)
• Have both white and black box tests been
specified?
• Have all independent logic paths been tested?
• Have test cases been identified and listed with
expected results?
• Is error handling to be tested?
• Are boundary values to be tested?
• Are timing and performance to be tested?
• Has acceptable variation from expected results
been specified?

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Maintenance
• Have side effects associated with change been
considered?
• Has the request for change been documented,
evaluated, and approved?
• Has the change, once made, been documented
and reported to interested parties?
• Have appropriate FTRs been conducted?
• Has a final acceptance review been conducted
to assure that all software has been properly
updated, tested, and replaced?

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Formal Technical Review
(FTR)
• Software quality assurance activity that is performed by
software engineering practitioners
– Uncover errors in function, logic, or implementation for
any representation of the software
– Verify that the software under review meets its
requirements
– Assure that the software has been represented according
to predefined standards
– Achieve software that is developed in a uniform manner
– Make projects more manageable
• FTR is actually a class of reviews
– Walkthroughs
– Inspections
– Round-robin reviews
– Other small group technical assessments of the software

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The Review Meeting
• Constraints
– Between 3 and 5 people (typically) are involved
– Advance preparation should occur, but should involve no
more that 2 hours of work for each person
– Duration should be less than two hours
• Components
– Product - A component of software to be reviewed
– Producer - The individual who developed the product
– Review leader - Appointed by the project leader; evaluates
the product for readiness, generates copies of product
materials, and distributes them to 2 or 3 reviewers
– Reviewers - Spend between 1 and 2 hours reviewing the
product, making notes, and otherwise becoming familiar
with the work
– Recorder - The individual who records (in writing) all
important issues raised during the review

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Review Reporting and
Recordkeeping
• Review Summary Report
– What was reviewed?
– Who reviewed it?
– What were the findings and conclusions?
• Review Issues List
– Identify the problem areas within the
product
– Serve as an action item checklist that
guides the producer as corrections are
made

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Guidelines for FTR
• Review the product, not the producer
• Set an agenda and maintain it
• Limit debate and rebuttal
• Enunciate the problem areas, but don’t attempt to solve
every problem that is noted
• Take written notes
• Limit the number of participants and insist upon
advance preparation
• Develop a checklist for each product that is likely to be
reviewed
• Allocate resources and time schedules for FTRs
• Conduct meaningful training for all reviewers
• Review your earlier reviews (if any)

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Reviewer’s Preparation
• Be sure that you understand the context of
the material
• Skim all product material to understand the
location and the format of information
• Read the product material and annotate a
hardcopy
• Pose your written comments as questions
• Avoid issues of style
• Inform the review leader if you cannot prepare

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Results of the Review
Meeting
• All attendees of the FTR must make a decision
– Accept the product without further modification
– Reject the product due to severe errors (and perform
another review after corrections have been made)
– Accept the product provisionally (minor corrections
are needed, but no further reviews are required)
• A sign-off is completed, indicating
participation and concurrence with the review
team’s findings

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Software Reliability
• Probability of failure-free operation for a
specified time in a specified environment.
• This could mean very different things for
different systems and different users.
• Informally, reliability is a measure of the
users’ perception of how well the software
provides the services they need.
– Not an objective measure
– Must be based on an operational profile
– Must consider that there are widely varying
consequences for different errors

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IO Mapping
Input Set
Output Set
Software
Subset of inputs
causing erroneous
outputs
Erroneous
outputs

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Software Faults and Failures
• A failure corresponds to erroneous/unexpected runtime
behavior observed by a user.
• A fault is a static software characteristic that can cause a
failure to occur.
• The presence of a fault doesn’t necessarily imply the
occurrence of a failure.
User A
Inputs
User B
Inputs
User C
Inputs
Erroneous
Inputs
Input Set

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Reliability Improvements
• Software reliability improves when faults
which are present in the most frequently used
portions of the software are removed.
• A removal of X% of faults doesn’t necessarily
mean an X% improvement in reliability.
• In a study by Mills et al. in 1987 removing
60% of faults resulted in a 3% improvement
in reliability.
• Removing faults with the most serious
consequences is the primary objective.

05_SQA_Overview.ppt

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05_SQA_Overview.ppt