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Software Quality EngineeringCS410

Class 5

Seven Basic Quality Tools

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Seven Basic Quality Tools• Promoted by Ishikawa (1989)

• Set of statistical tools for quality control

• Can be used to analyze software metrics

• Most applicable to Project Managers

• Statistical process control for SW development is more challenging than traditional manufacturing

• Tools can have a positive influence on quality improvement and decision making

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Seven Basic Quality Tools• Seven Tools

1. Checklist (or Check Sheet)

2. Pareto Diagram

3. Histogram

4. Scatter Diagram

5. Run Chart

6. Control Chart

7. Cause-Effect Diagram

• Figure 5.1 p. 130

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Checklist• A paper (or softcopy) form used for collecting and

arranging data so that it can be easily used later• Also a method for ensuring that key points and

tasks are addressed, or performed, at the correct times

• Also a method to assist in knowing when a particular task is complete

• Can be implemented as an expert system to guide process and give advise

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Checklist• Checklist examples:

– Common Error Checklist - developed as part of DPP, used at stage kickoff to review common errors at that stage

– Process Checklists• Program Fix Checklists - ensure that all the required

steps for completing a fix have been done (example fig. 5.2 pp132-133)

• Code Complete Checklists - ensure that all coding standards and procedures have been followed

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Pareto Diagram• Pareto Principle (80/20 rule)

– 80% of the defects are contained in 20% of the modules and components

– 20% of a particular defect type cause 80% of the customer calls

• Pareto analysis helps identify focus areas that cause most of the problems

• Pareto Analysis can be charted as frequencies in descending rank order with a cumulative percentage line (fig 5.3 p. 134 and fig. 5.4 p. 136)

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Histogram• A graphic representation of frequency

distribution

• Should convey complete information at a glance

• Examples:– Defect distributions by Sev level (fig. 5.5(A) p. 137)

– Defect distribution by days open (fig. 5.5(B) p. 137)

– Profile of Customer Satisfaction (fig. 5.6 p. 137)

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Run Charts• A real-time statement of quality and/or

workload.– Defect arrival rates weekly– Defect backlog– Delinquent fixes

• Should include target for comparison

• Can track significant events, and show results

• Figure 5.7 p. 138

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Run Charts• Good tool for project and schedule

management.

• Run Chart can display the typical “S” Curve

• Tracks actual vs. planned over time– Completion of design review– Completion of code inspection– Completion of code integration– Completion of component test– Completion of system test– etc.

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Scatter Diagrams• Usually relates to investigative work (I.e.

investigating relationships)• Requires precise data• Works well for correlation analysis• For example: Code complexity vs. Defect Rate

(fig 5.9 p. 140)– Shows positive correlation– Can be used as a predictor– Can be used as a tool to reduce defect rate (by

reducing code complexity)

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Scatter Diagrams• Can also be used for identifying/prioritizing

areas requiring action items

• For example: Defects rates for reused components in multiple projects (fig. 5.10 p. 141, and fig. 5.11 p. 142)– Helps identify chronic problem components– Helps focus action items on greatest payback

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Control Chart• A tool used in Statistical Process Control (SPC)• Can be used real-time for improving consistency

and stability• A tool for measuring Process Capability

– Process Capability - inherent variation in the process in relation to the specification limits

– The smaller the process variation the better the process’s capability

• Process Capability is a difficult thing to estimate in software projects, however Control Charts are a useful quality management tool.

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Control Chart• Types of control charts

• X-bar - sample averages

• S chart - standard deviations

• Median chart - individuals

• P chart - proportion nonconforming

• NP chart - number nonconforming

• C chart - number nonconformities

• U chart - nonconformities per unit

• Most appropriate to SW Engineering– P chart - when percentages are involved– U chart - when defect rates are involved

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Control Chart• Control limits must be calculated and included

on the chart

• Different ways of calculating control limits exists.

• Historical data• Weighted averages• Standard Deviations

• SW metrics that can be control charted• Defects per component/KLOC (fig. 5.12 p. 146)• Phase effectiveness (fig. 5.14 p. 147)• Backlog Management Index

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Cause-Effect Diagram• Also known as a Fishbone Diagram

• Not widely used in SW development

• Graphically relates causes and effects

• Effect can be a positive or negative characteristic

• Examples– Register Allocation Defects (negative) fig. 5.15 p. 148

– Effective Inspections (positive) fig 5.16 p. 149

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Seven Basic Quality Tools Summary

• Statistical tools (scientific methods) are used heavily in manufacturing, and are slowly being incorporated into SW engineering.

• Some tools can be used together effectively:– Pareto Diagrams, Cause-Effect Diagrams, and Scatter

Diagrams, can be used together to identify dominant problems and their root causes.

• Control Charts can be used to monitor process stability.

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Seven Basic Quality Tools Summary

• Keys to a tool’s value:– Consistent use

– Pervasive use

– Automation

– Integration

– As a tool for process improvement

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Seven Basic Quality Tools Summary

• Ishikawa’s Tools a.k.a. “Seven Old Tools”• Other tools - “Seven New Tools”

• Affinity Diagram• Relations Diagram• Tree Diagram• Metric Chart• Matrix Data Analysis Chart• Process Decision Program Chart• Arrow Diagram