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©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 24Slide 1 Chapter 24 Quality Management.

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Presentation on theme: "©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 24Slide 1 Chapter 24 Quality Management."— Presentation transcript:

1 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 24Slide 1 Chapter 24 Quality Management

2 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 24Slide 2 l A software property can be measured l The relationship exists between what we can measure and what we want to know l This relationship has been formalized and validated l It may be difficult to relate what can be measured to desirable quality attributes Metrics assumptions

3 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 24Slide 3 Internal and external attributes

4 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 24Slide 4 The measurement process l A software measurement process may be part of a quality control process l Data collected during this process should be maintained as an organisational resource l Once a measurement database has been established, comparisons across projects become possible

5 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 24Slide 5 Product measurement process

6 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 24Slide 6 Data collection l A metrics programme should be based on a set of product and process data l Data should be collected immediately (not in retrospect) and, if possible, automatically l Three types of automatic data collection Static product analysis Dynamic product analysis Process data collation

7 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 24Slide 7 Automated data collection

8 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 24Slide 8 Data accuracy l Dont collect unnecessary data The questions to be answered should be decided in advance and the required data identified l Tell people why the data is being collected It should not be part of personnel evaluation l Dont rely on memory Collect data when it is generated not after a project has finished

9 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 24Slide 9 l A quality metric should be a predictor of product quality l Classes of product metric Dynamic metrics which are collected by measurements made of a program in execution Static metrics which are collected by measurements made of the system representations Dynamic metrics help assess efficiency and reliability; static metrics help assess complexity, understandability and maintainability Product metrics

10 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 24Slide 10 Dynamic and static metrics l Dynamic metrics are closely related to software quality attributes It is relatively easy to measure the response time of a system (performance attribute) or the number of failures (reliability attribute) l Static metrics have an indirect relationship with quality attributes You need to try and derive a relationship between these metrics and properties such as complexity, understandability and maintainability

11 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 24Slide 11 Software product metrics

12 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 24Slide 12 Object-oriented metrics

13 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 24Slide 13 Measurement analysis l It is not always obvious what data means Analysing collected data is very difficult l Professional statisticians should be consulted if available l Data analysis must take local circumstances into account

14 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 24Slide 14 Measurement surprises l Reducing the number of faults in a program leads to an increased number of help desk calls The program is now thought of as more reliable and so has a wider more diverse market. The percentage of users who call the help desk may have decreased but the total may increase A more reliable system is used in a different way from a system where users work around the faults. This leads to more help desk calls

15 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 24Slide 15 Key points l Software quality management is concerned with ensuring that software meets its required standards l Quality assurance procedures should be documented in an organisational quality manual l Software standards are an encapsulation of best practice l Reviews are the most widely used approach for assessing software quality

16 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 24Slide 16 Key points l Software measurement gathers information about both the software process and the software product l Product quality metrics should be used to identify potentially problematical components l There are no standardised and universally applicable software metrics


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