Chapter 7.2.ppt

OHT 7.1

Galin, SQA from theory to implementation © Pearson Education Limited 2004

Continuing:

•Factors affecting intensity of SQA activities •Verification, validation and qualification

•Development and quality plans for small and for internal projects

•A model for SQA defect removal effectiveness and cost

Chapter 7.2

OHT 7.2


Factors affecting Intensity of SQA Activities • SQA Activities are linked to the completion of a project

phase– Requirements, design, etc.

• The SQA activities need to be integrated into the development plan that implements one or more software development models, such as the waterfall, prototyping, spiral, …

• They need to be activities just like other more traditional activities – be entered in plan, scheduled, etc.

OHT 7.3


Factors affecting Intensity of SQA Activities • SQA planners need to determine

– A list of SQA activities needed for the project– And then for each activity, they need to decide on

• Timing• Type of QA activity to be applied (there are several) • Who performs the activity and resources required.

– Important to note that many participate in SQA activities

» Development team

» Department staff members

» Independent bodies

• Resources required for the removal of defects and introduction of changes.

OHT 7.4


Factors affecting Intensity of SQA Activities • Sad testimony that few want to allocate the

necessary time for SQA activities. – This means time for SQA activities and then

time for subsequent removal of defects.– Often, there is no time for follow-on work!!

• Activities are not simply cranked in and absorbed!

• So, time for SQA activities and defect correction actions needs to be examined.

OHT 7.5


Factors Affecting the Required Intensity of QA Activity

• Project Factors– Magnitude of the project – how big is it?

– Technical complexity and difficulty Discuss– Extent of reusable software components – a real factor

– Severity of failure outcomes if project fails – essential!

• Team Factors– Professional qualifications of the team members

– Team acquaintance w/ project and experience in the area

– Availability of staff members who can professionally support the team, and

– Percentage of new staff members in the team.

OHT 7.6


So, what are the activities??• Recognize that these activities take days to undertake, and

days to correct. Here are some sample activities:

• (and don’t forget the planning for the reviews, materials, …)

• Design Review of Requirements

• Design Review of xxxxx

• Design Review of ….

• Inspections of ….

• Inspections of …..

• Unit Testing of software code for each interface module …

• Unit testing of ….

• System Testing of ….

• Design Review of User’s Manual…..

OHT 7.7


Verification – The process of evaluating a system or component to determine whether the products of a given development phase satisfy the conditions imposed at the start of that phase

Validation - The process of evaluating a system or component during or at the end of the development process to determine whether it satisfies specified requirements

Qualification - The process used to determine whether a system or component is suitable for operational use

IEEE Std 610.12-1990 (IEEE 1990)

Verification, Validation, and Qualification

Three aspects of Quality Assurance for Software Products:

OHT 7.8


More on VV and Q• Verification looks at the consistency of the products being developed with

products developed in previous phases.

• Developers verify as we go.

• Validation is a customer thing – customers validate the outputs, etc. Validate against their original requirements.

• Necessary for customer satisfaction.

• Qualification focuses on operational aspects – maintenance is the main issue.

• Has development taken place IAW professional standards and procedures such that follow-on maintenance is easier to undertake?

• Planners need to determine which of all these need to be examined in each QA activity.

OHT 7.9


The model addresses two quantitative aspects of the SQA planning addressing several defect detection activities.

a.Want to study the SQA plan’s total effectiveness in removing project defects, and

b.The total costs of removal of project defects

Note again that SQA activities must be integrated within the project’s development plan.

OHT 7.10


Model for Defect RemovalThe data:

Model based on three types of data:

Defect origin distribution

in which phase did the defects occur

Defect removal effectiveness, and

how effective are we at removal of defects?

Cost of defect removal.

how much does it cost per defect per phase!!!

OHT 7.11


Defect Origin Distribution

• Very consistent over many years:

• Distribution of Defects:– Requirements Specs 15%– Design 35%– Coding / integration 40%– Documentation 10%

OHT 7.12


Defect Removal Effectiveness• Generally speaking, the percentage of removed defects is

lower than the percentage of detected defects, because some corrections are ineffective or inadequate.

• We simply miss some!!

• Others are undetected and uncorrected and passed on to successive development phases.

• Lingering defects coupled with introduced defects in current development phase add up!!!

• For discussion purposes, we will assume the filtering effectiveness of accumulated defects of each quality assurance activity is not less than 40%, that is, each activity removes at least 40% of the incoming defects.

OHT 7.13


Defect Removal Effectiveness• Removal effectiveness

– QA Activity Average defect filtering effectiveness rate

requirements specs review 50%

design inspection 60%

design review 50%

code inspections 65%

unit test 50%

Unit test > code review 30%

integration test 50%

system tests / acceptance 50%

documentation review 50%

OHT 7.14


Cost Removal• Removal of defects differs very

significantly by development phase.

• Cost are MUCH greater in later development phases.

• Note: In general, defect removal data is not commonly available.

• Most agree with the data based on key studies. (next slide)

OHT 7.15


Defect removal phase Defect removal

effectiveness

Average relative defect removal cost {cost unit}

Defect origination phase

Req Des Uni Int Doc

Requirement specification (Req) 50% 1 --- --- --- ---

Design (Des) 50% 2.5 1 --- --- ---

Unit coding (Uni) 50% 6.5 2.6 1 --- ---

Integration (Int)System documentation (Doc)

50%50%

1616

6.46.4

2.52.5

11

System testing / Acceptance testing (Sys)

50% 40 16 6.2 2.5 1

Opertion by customer (after release)

100% 110 44 17 6.9 2.5

OHT 7.16


The ModelOur Model is based on following assumptions:•Development process is linear, sequential following waterfall model•There is a number of new defects introduced each phase•Review and test software quality assurance activities serve as filters, removing a percentage of defects and letting the rest pass to next development phase as we saw three slides back.•At each phase, incoming defects are the sum of those not removed plus new defects in current phase•Cost of defect removal is calculated for each SQA activity by multiplying the number of defects removed by the relative cost of removing a defect. (see table, previous slide)•Remaining defects are passed to the customer. (this is the heaviest cost for defect removal)

OHT 7.17


Model - parameters• The models we show use these parameters:

– POD – Phase originated defects– PD – Passed defects (from former phases)– %FE - % of filtering effectiveness– RD – Removed defects– CDR – Cost of defect removal– TRC – Total Removal Costs

OHT 7.18


First Model (standard)• This model applies a standard quality assurance plan

(standard defects filtering system) composed of QA activities, that is, ‘filters’ we have:

QA activity removal effectiveness Cost of removing defect

– Requirements Spec review 50% 1

– Design Review 50% 2.5

– Unit Test 50% 6.5

– Integration tests 50% 16

– Documentation Review 50% 16

– System Test 50% 40

– Operation Phase 100% 110

OHT 7.19


• Using the standard quality assurance plan’s quality assurance activities on previous slide, a process-oriented illustration of the standard QA plan model follows:

OHT 7.20


POD – phase originated defectsPD – passed defects%FE – percent filteringRD – removed defectsCDR - Cost of removing defectsTRC - Total Cost of Defect Removal

OHT 7.21


Costs of Defect Removal• But we can do better using a comprehensive quality

assurance plan with more activities, and hence better filtering.

• The comprehensive quality assurance plan (comprehensive defects filtering system) accomplishes the following:

• 1. Adds two quality assurance activities so that the two are performed in the design phase as well as in the coding phase– We have a Design Inspection and a Design Review vice Design, and

– Code Inspections and unit test vice simple Unit Test

• 2. Improves the ‘filtering’ effectiveness of other quality assurance activities.

OHT 7.22


Comprehensive Quality Assurance Plan:

POD – phase originated defectsPD – passed defects%FE – percent filteringRD – removed defectsCDR - Cost of removing defectsTRC - Total Cost of Defect Removal

Design Inspect and Design Review

Code inspectionprecedes unit test

OHT 7.23


Comprehensive Plan • Conclusions:• The standard plan successfully removes 57.6% of the defects in

requirements and design compared to 90.2% in the comprehensive plan before coding begins.– Results from more intensive defect-removal efforts.

• The comprehensive plan as a whole is much more economical than the standard plan as it saves 41% of the total resources investing in defect removal, compared with the standard plan

• Compared to the standard plan, the comprehensive plan makes a greater contribution to customer satisfaction by drastically reducing the rate of defects detected during regular operations: 6.9% to 2.6%

OHT 7.24


Conclusion

• So, in general, the quantitative results of the comparison comply nicely with the SQA approach.

• Additional investments in QA activities yield substantial savings in defect removal costs.

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Chapter 7.2.ppt