Support for Assurance Case Maintenance

Throughout the operational life of any system, changing regulatory requirements, additional assurance evidence and a changing design can challenge the corresponding assurance case. In order to maintain an accurate account of the assurance of the system, all such challenges must be assessed for their impact on the original assurance argument.

Why do we need maintenance?

An assurance case consists of many inter-dependent parts: requirements, argument, evidence, design and process information. As a result, a single change to an assurance case may necessitate many other consequential changes - creating a 'ripple effect'. It is significant to recognize the importance of every challenge to an assurance case. Furthermore, the indirect impact is crucial and one of the biggest challenges. Any of these challenges imply re-certification and by extension re-generation of the assurance case of a system. The construction and maintenance of assurance case arguments is expensive and tedious, as it is mainly a manual process that requires a considerable amount of time. Therefore, offering safety engineers tool-supported re-evaluation is a big step forward.

Change Impact Analysis for Assurance Cases

The change impact analysis includes the handling of challenges regarding the following different argument elements.

Potential vs. actual change effect

The rules described above constitute the potential change effect and not necessarily the actual change. There is a significant difference between actual and potential change. The nodes to which the impact of the challenge in a connected GSN node propagates are called impacted nodes. The potential change includes further analysis of the possible effects on the rest of GSN nodes after one element is challenged. A safety engineer has to review all the potential challenges and decide upon them. ExplicitCase implements as a starting point, the potential change effect.

Change Impact Analysis in ExplicitCase

The assurance case maintenance in ExplicitCase requires the participation of different entities and stakeholders (see Fig. 8). The system modeling is done by the system engineer and the GSN modeling of the assurance cases by the safety engineer. The safety engineer has also responsibilities such as hyperlinking GSN with System Models and annotating GSN assurance cases with maintainability information. ExplicitCase recognizes challenges to validity of GSN assurance cases and identifies the impact of a GSN node challenge. Finally, the safety engineer gives input to the system engineer regarding the reasons why, after a change in one system model element, other system model elements, should be reviewed.

Fig. 8 - Stakeholders in ExplicitCase.

Steps

  1. Follow the steps in the section "Steps to specify the contained elements of a assurance case module" and build an assurance case module;
  2. Select the Solution Argument Element and right-click on it. Click 'Is Challenged';
  3. The challenged solution has changed its color to red;
  4. Right-click again on the challenged solution. Click 'Show potential change impact';
  5. The potentially impacted argument elements, by the challenged solution, have turned their color to yellow;