DEPENDABLE SYSTEMS

Nota:

• Dependability reflects a systems trustworthiness(no system failure), and can be divided into five main categories namely:

1. Safety
2. Reliability
3. Security
4. Resilience
5. Availability

Nota:

• These are broad systems that include both non-technical and technical components, all of which affect/influence the systems dependability. These systems can be viewed as layers of these various components, which make up the sociotechnical system stack

1. Data Management
2. Operating System
3. Equipment
4. Organization
5. Society
6. Business Processes
7. Application System
8. They include both non-technical and technical components, all of which influence the systems dependability.

Nota:

• Redundancy means extra components are included in the that can be used if part of the system fails. Diversity means there are different types of redundant components used, in order to reduce the chances of a system failure.

Nota:

• Software processes designed to produce dependable systems. So investing in dependable processes is a good idea because this will likely lead to the delivery of software that is reliable. e.g prog testing to find errors - Process used depends on the type of system being built

1. These are processes designed to produce dependable systems e.g program inspection and testing to find errors

Nota:

• Researchers have advocated for formal methods, where a formal model of a system is used as a basis for development, to help reduce specification and implementation errors - thus increasing system dependability -Effective for discovering or avoiding two classes of errors with the software, namely: (Adv. - Disad.)

1. Specification and Design Errors
2. Inconsistencies between a specification and a program

   Nota:

   • Mistakes made by the developer that make the software inconsistent with the specification are avoided