IEC 62741 pdf download.Demonstration of dependability requirements – The dependability case
1 Scope
This International Standard gives guidance on the content and application of a dependability case and establishes general principles for the preparation of a dependability case. This standard is written in a basic project context where a customer orders a system that meets dependability requirements from a supplier and then manages the system until its retirement. The methods provided in this standard may be modified and adapted to other situations as needed. The dependability case is normally produced by the customer and supplier but can also be used and updated by other organizations. For example, certification bodies and regulators may examine the submitted case to support their decisions and users of the system may update/expand the case, particularly where they use the system for a different purpose.
4 Background to the dependability case
4.1 Principles and purpose A dependability case provides a reasoned and traceable argument based on evidence that a system satisfies the requirements and will continue to do so over time. It demonstrates why certain activities have been undertaken and how they can be judged to be successful. For maximum effectiveness it should be initiated at the concept stage, revised progressively during a system life cycle and is typically summarized in dependability case reports at predefined milestones. It records progress in obtaining evidence that dependability requirements are met and remains with the system throughout its life cycle until retirement.The dependability case is of the greatest benefit for high value, low quantity systems where direct evidence of dependability may be difficult or expensive to obtain. Since these systems are often highly complex, involve novel technologies and have wide-ranging stakeholders, an explicit argument is necessary in order to demonstrate their detailed dependability claims with suitable evidence. 4.2 Relationship between the dependability case and dependability plans Effective management of dependability requires organizational arrangements to implement policy, activities implemented in dependability programmes and plans and processes for performance evaluation, assurance and review. A dependability programme involves a) dependability plans, that define the activities, techniques and resources required to achieve dependability, b) methods for measurement and assessment, c) assurance and review. The objectives of a dependability plan include ensuring that 1 ) the dependability requirements of the customer are determined and demonstrated to be understood by both the customer and supplier, 2) activities are planned, agreed and implemented to satisfy and demonstrate the requirements and treat the risks of failure, 3) the customer is provided with assurance that the dependability requirements are being, or will be, satisfied and that uncertainty in the dependability decreases over the course of the plan. The dependability case provides progressive assurance that dependability requirements are being or will be satisfied and that uncertainty in the dependability is decreasing. In addition, the case demonstrates that the activities in the plan achieve the requirements and treat the risks. This forms part of the argument and evidence for why the system is, or will be, dependable. The plan is usually based on standards and the organization’s experience in managing dependability and is tailored, taking into account factors such as the relevant life cycle stages.The dependability plan and dependability case are often developed concurrently as both include consideration of the risks of not meeting the requirements. However, the system might meet the dependability requirements but it might not be possible to demonstrate that these requirements have been met. This might be because there is no appropriate activity which can demonstrate that the requirements have been met, or the cost or time required to do so might be excessive. Therefore the dependability plan may also include activities specifically intended to treat the risks of not being able to demonstrate that the requirements have been met and these activities also provide evidence in the dependability case. A register of risks produced as part of a dependability case should be coordinated with the risks identified as part of planning the dependability programme and with the project risk register. Activities proposed to treat the risks are included in the dependability plan and examined as sources of evidence that risks have been treated. As the dependability plan is implemented, the dependability case is populated with evidence of the successful implementation of the plan. This provides progressive assurance that requirements are being met. If sufficient evidence is not able to be obtained, then the dependability plan should be modified accordingly.
IEC 62741 pdf download
