Software Engineering Modern Approaches Eric Braude and Michael Bernstein 1

© 2010 John Wiley & Sons Ltd. Chapter 2. Software Quality 2

The Software Development Lifecycle What does “software quality” mean? What are “defects” in applications What is the difference between verification and validation in software development? How do you measure software quality? Requirements analysis Design Implementation Testing Maintenance Planning 3

© 2010 John Wiley & Sons Ltd. Software Quality The more closely a software product meets its specified requirements, and those requirements meet the wants and needs of its customers, the higher its quality. 4

The Meaning of “Software Quality” 100% 0% Graphics courtesy Corel Requirements (explicit and implicit) Typical quality focus © 2010 John Wiley & Sons Ltd. 5

Software Quality (cont.) Software will contain defects Defect: deviation from requirement Software quality concerns the severity and extent of defects 6

© 2010 John Wiley & Sons Ltd. Software Quality (cont.) Quality goals: 1.Remove as many defects as is reasonably possible before project is completed 2.Remove as many of these defects as early in the development process as possible  Cost to repair increases the later a defect is discovered 7

© 2010 John Wiley & Sons Ltd. Software Quality (cont.) Moral of the story: –Finding defects early is easier and saves $$$ 8

Defect Repair Cost Requirements Design ImplementationTest Maintenance © 2010 John Wiley & Sons Ltd. 9

Phases Requiring Quality and Metrics Design Integration and System Testing Planning Requirements Analysis Maintenance Implementation and Unit Testing Process 10

© 2010 John Wiley & Sons Ltd. Verification and Validation (V&V) Verification: Ensuring that each artifact is built in accordance with its specifications - “Are we building the product right?” -Mostly inspections and reviews Validation: Checking that each completed artifact satisfies its specifications - “Are we building the right product?” - Mostly testing 11

© 2010 John Wiley & Sons Ltd. Creation, Verification and Validation Partially completed artifact Artifact under construction Completed artifact creationvalidation process verification Software engineer Graphics courtesy of Corel 12

© 2010 John Wiley & Sons Ltd. Quality Documentation  Software Quality Assurance Plan (SQAP) –IEEE Std –Overall approach to quality  Software Verification and Validation Plan (SVVP) –IEEE Std –V &V practices 13

© 2010 John Wiley & Sons Ltd. Metrics  Numerical measures that quantify the degree to which software or a process possesses a certain attribute –e.g. Defects/KLOC –e.g. Average module size  Collected and analyzed throughout software project 14

© 2010 John Wiley & Sons Ltd. Metrics (cont.)  Benefits and uses: –Measure software quality level –Estimate project schedules –Track schedule progress –Measure software size and complexity –Determine project cost –Process improvement 15

© 2010 John Wiley & Sons Ltd. Quality Metrics  Defect density  Mean time to failure  Customer problems  Customer satisfaction 16