AS IEC 60300.3.15:2011 pdf – Dependability managementPart 3.15:Application guide— Engineering of system dependability.
Adopting an infrastructure using methodology such as the Capability Maturity Models as a framework for software development can facilitate the achievement of dependability in software functions. Software issues and versions for upgrades should be controlled by a system configuration management process to sustain interoperability of functions and enhance dependability in performance;
c) Human element — human interactions with system operation can be viewed as part of the system functions or as an end user of the system. The role of the human in system performance can be beneficial with the human’s ability to mitigate or control the on-going situations. However, most industrial incidents reported and major accidents studied can be traced back to human errors as the primary cause of system malfunction or disruption in performance service. Systems designed for human operation or use should incorporate human factors in the system design to minimize the risk of critical system failures, loss of properties, security violations or safety threats. Dependability can be achieved by application of human factors in design rules and simplification of tasks for human operation. The study of human factors involves a multi-disciplinary effort on gathering information about human capabilities and limitations for applications affecting human- system performance. The engineering aspects consist of the application of human factors information to the design of tools, machines, systems, tasks, jobs, and environment for safe, comfortable, and effective human use. Training and education are important prerequisites for any system operation requiring human interaction. Human factors standardization facilitates system integration, enhances interoperability of system elements, and improves serviceability and overall dependability performance.
Most system functions in today’s electronic products use combined hardware and software elements in system designs. They offer a broad range of design features for diverse applications. Dependability of system functions is achieved by incorporation of design rules and established processes for applications. Design trade-off can be attained by proper combination of technologies suitable to meet specific application needs. Economic values can be gained through modular packaging and standardization for mass-scale production. System functions can be automated for self-checking to improve performance effectiveness by means of built-in-test or other monitoring schemes. Human intervention in system functions is only necessitated by safety and security regulations, or dictated by social and economic reasons. Annex D provides checklists for hardware, software, and human factor design applications.
6.2.5 Approaches to determine achievement of system dependability
There are three generic approaches to determine that system dependability has been achieved. They serve different purposes with varying degree of engineering rigour. In practice, a combination of these approaches is likely to be used:
a) Demonstration — this is achieved by means of actual system operation in an application environment over a scheduled time period to demonstrate dependability performance. Typical examples include:
— dependability performance history of systems in field operation;
— formal reliability demonstration;
— availability performance during warranty period.
b) Inference — this is achieved by means of statistical methods using observed data of
constituent system functions based on established criteria and assumptions to arrive at a
numerical value representing system dependability attributes (characteristics /
performance). Typical examples include:
— prediction of system of given configuration;
— system simulation;
— capability maturity models;
— test case verification of system performance.
6.2.6 Objective evidence of achievements
The following are key statements on system dependability characteristics for use as objective evidence to support system and product acceptance at applicable system life cycle stages. Objective evidence needs to be documented and authenticated for auditing and contracting purposes.
a) a statement on system dependability attributes and operating environment to reflect user expectations in commercial specification or proposal based on market research information. This provides information to start project planning and develop system dependability specification;
b) a statement on system performance characteristics in system dependability specification. This provides information for establishing dependability design objectives and system architecture;
c) a statement on reliability and maintainability performance characteristics for each system function in functional design specification. This provides information for technology selection, make-buy decisions, and establishing procurement requirements;
d) a statement on reliability and maintainability characteristics for system in-service operation and maintenance. This provides information for logistics support planning, contract maintenance, and special training needs.