Safety assurance cases provide structured justifications that safety-critical systems meet their safety requirements. Recently, the notion of defeaters has emerged as a rigorous means of challenging the validity of safety arguments. Examples of defeaters might include overly strict claims, unreliable evidence, or reasoning gaps. However, defeaters remain ad hoc, lack structured support for critical reflection, are inconsistently described, are difficult to review, and lack documentation standards. To address this, we propose Defeater Cards, a new structured documentation artifact for systematically characterizing, reasoning about, and managing defeaters in safety cases. Drawing on a literature survey and thematic analysis, we identify documentation criteria that inform the card's structure, based on the 5W1H framework. Defeater Cards are designed to support informed analysis and evolution, improve traceability and auditability, and enable the reuse of defeater knowledge across systems and product variants. We demonstrate their applicability through two cross-domain case studies, showing how they expose hidden assumptions, surface reasoning gaps, and support ongoing safety assurance case evolution. To support adoption and community reuse, we also release an open-source repository of defeater cards as a baseline upon which researchers and practitioners can build and describe lessons learned.

翻译：安全保证案例为关键安全系统满足其安全需求提供了结构化的论证依据。近年来，"反证特征"（defeaters）的概念被提出，作为对安全论证有效性进行严格质疑的手段。反证特征的实例可能包括过于严苛的声明、不可靠的证据或推理缺陷。然而，当前反证特征的处理仍存在临时性、缺乏批判性反思的结构化支持、描述不一致、难以审查以及缺少文档规范等问题。为解决这些问题，我们提出反证卡片（Defeater Cards）——一种新的结构化文档产物，用于系统地表征、推理和管控安全案例中的反证特征。基于文献调查与主题分析，我们依据5W1H框架确定了文档化准则，用以指导卡片结构设计。反证卡片旨在支持有依据的分析与演化、提升可追溯性与可审计性，并实现跨系统及产品变体中反证知识的复用。通过两个跨领域案例研究，我们展示了其如何揭示隐藏假设、暴露推理缺陷，并支持安全保证案例的持续演化。为促进采纳与社区复用，我们还开源了反证卡片知识库，作为研究者与实践者构建经验与描述教训的基线。