Cloud computing technologies can be used to store a tremendous amount of learning resources, including educational videos. However, it is difficult for users to retrieve relevant teaching material in cloud environments by submitting a few keywords. We propose a search mechanism based on social networks. Furthermore, the issues of availability and trustworthiness have to be considered in teaching material retrieval process, in order to improve the retrieval performance. Current P2P file sharing applications focus on exact matching and ignore the dynamic nature inherent in P2P networks, which might degrade the retrieval performance in terms of precision and response time. Our idea is to appropriately set the due time to improve response time of P2P teaching material retrieval without sacrificing much precision. In this study, we formulate the due time setting problem as a bi-objective optimization problem and approximately solve it by an interaction-based heuristic method. The proposed approach consists of two phases: construction phase and sharing phase. In construction phase, peer information is acquired and managed in a decentralized manner. In sharing phase, the due time is interactively determined and the results are retrieved. A prototype of cloud platform has been constructed and experiments have been conducted to evaluate the performance of the approach. The experimental results show that the interactive algorithm performs well in P2P networks with low trust and availability. Also, a survey of satisfaction shows that the proposed method is more user-friendly.
