Chapter 10 – Dependable systems. The lecture discuss the key metrics used for different phases of software development. In this chapter, the following content will be discussed: Version control, change control, configuration audit, status reporting, configuration management for WebApp. | Chapter 10 – Dependable systems 30/10/2014 Chapter 10 Dependable Systems 1 Topics covered Dependability properties Sociotechnical systems Redundancy and diversity Dependable processes Formal methods and dependability 30/10/2014 Chapter 10 Dependable Systems 2 System dependability For many computer-based systems, the most important system property is the dependability of the system. The dependability of a system reflects the user’s degree of trust in that system. It reflects the extent of the user’s confidence that it will operate as users expect and that it will not ‘fail’ in normal use. Dependability covers the related systems attributes of reliability, availability and security. These are all inter-dependent. 3 Chapter 10 Dependable Systems 30/10/2014 Importance of dependability System failures may have widespread effects with large numbers of people affected by the failure. Systems that are not dependable and are unreliable, unsafe or insecure may be rejected by their users. The costs of system failure may be very high if the failure leads to economic losses or physical damage. Undependable systems may cause information loss with a high consequent recovery cost. 4 Chapter 10 Dependable Systems 30/10/2014 Causes of failure Hardware failure Hardware fails because of design and manufacturing errors or because components have reached the end of their natural life. Software failure Software fails due to errors in its specification, design or implementation. Operational failure Human operators make mistakes. Now perhaps the largest single cause of system failures in socio-technical systems. 5 Chapter 10 Dependable Systems 30/10/2014 Dependability properties 30/10/2014 Chapter 10 Dependable Systems 6 The principal dependability properties 30/10/2014 Chapter 10 Dependable Systems 7 Principal properties Availability The probability that the system will be up and running and able to deliver useful services to users. Reliability The probability that the system will . | Chapter 10 – Dependable systems 30/10/2014 Chapter 10 Dependable Systems 1 Topics covered Dependability properties Sociotechnical systems Redundancy and diversity Dependable processes Formal methods and dependability 30/10/2014 Chapter 10 Dependable Systems 2 System dependability For many computer-based systems, the most important system property is the dependability of the system. The dependability of a system reflects the user’s degree of trust in that system. It reflects the extent of the user’s confidence that it will operate as users expect and that it will not ‘fail’ in normal use. Dependability covers the related systems attributes of reliability, availability and security. These are all inter-dependent. 3 Chapter 10 Dependable Systems 30/10/2014 Importance of dependability System failures may have widespread effects with large numbers of people affected by the failure. Systems that are not dependable and are unreliable, unsafe or insecure may be rejected by their users. The .
