Publishing information to clients of an information system may leak confidential information. Even more, update transaction protocols must ensure both integrity and confidentiality of information, which results in a conflicting situation rather involved. To avoid confidentiality breaches previous works allow views with misinformation provided to clients. In order to maintain correctness and reliability of information, we propose query and update protocols that refuse client requests for the sake of confidentiality. Further, this article focuses on availability of information in two ways: confidentiality policy specification can impose less strict confidentiality in favor of availability; the proposed transaction protocol is shown to be as cooperative and to provide as much information as possible among a discussed class of transaction protocols. Regarding the confidentiality policy, in our approach the security administrator can choose between protecting only sensitive information in the current instance or even outdated information of previous instances.