Abstract: When resources are denied access, users usually receive “access denied” feedback messages with no specific reasons, which makes the legitimate resources requesters be refused by system with no apparent reasons, and affects the friendliness of human-computer interaction and the efficiency and success rate during negotiation. For that reason, a feedback mechanism is proposed, which is applied on access denied, and a feedback model is built according to the identity of users and environment of system. Example shows that the model can provide useful and suitable feedback information based on the identity of users and environment of system, under the premise of non-disclosure of sensitive information and policies.

Key words: feedback model, trust negotiation, cost tree, minimal cost

摘要： 资源在被拒绝访问时，用户通常接收到的反馈信息是无具体原因的“拒绝访问”，使得合法的资源请求者无来由地被系统拒绝，影响了人机交互的友好性以及信任协商过程中的效率和成功率。提出一种针对在资源被拒绝访问时应用的反馈机制，根据资源请求者的身份和当前的系统环境这两个重要因素，建立一个反馈模型。实例证明该模型能够在不泄露敏感信息和策略的前提下，根据请求者的身份以及当前的系统状态提供有用而又适当的反馈信息。

关键词: 反馈模型, 信任协商, 代价树, 最小代价值