CS 325: Software Engineering March 26, 2015 Software Quality Assurance Software Metrics Defect Injection Software Quality Lifecycle Measuring Progress Software Reliability

CS 325 March 26, 2015 Page 197 Software Metrics Measuring the quality of software is a difficult task, but efforts are being made to do so ISO 9126, an international standard for the evaluation of software, classifies software quality as a hierarchy of characteristics ISO 9126 Functionality * Suitability * Accuracy * Interoperability * Compliance * Security Reliability * Maturity * Recoverability * Fault Tolerance Usability * Learnability * Understandability * Operability Efficiency * Time Behavior * Resource Behavior Maintainability * Stability * Analyzability * Changeability * Testability Portability * Installability * Replaceability * Adaptability

CS 325 March 26, 2015 Page 198 Defect Injection Cutting corners in the early stages of software development tends to cause defects to be injected.

CS 325 March 26, 2015 Page 199 Software Quality Lifecycle Quality can be infused into a software product throughout its lifecycle. Plan Clarify goals Analyze risks Assign QA roles Plan Clarify goals Analyze risks Assign QA roles Verify/Validate Customize processes Peer reviews Examine alternatives Develop test cases Verify/Validate Customize processes Peer reviews Examine alternatives Develop test cases Improve Analyze reviews/tests Diagnose defect causes Repair, review, repeat Improve Analyze reviews/tests Diagnose defect causes Repair, review, repeat Manage Status reports Manage resources Manage Status reports Manage resources

CS 325 March 26, 2015 Page 200 Measuring Progress A variety of metrics may be used to determine how a project is progressing Time invested Lines of code Reused lines of code Changed lines of code Number of modules Size of database Defect count Collecting measurements isn’t enough - reviewing them is essential to determining whether a project is on track

CS 325 March 26, 2015 Page 201 Software Reliability Once installed, the reliability of a software system may be measured via the mean time to repair (MTTR), the mean time to failure (MTTF), and their sum, the mean time between failures (MTBF).