Information systems are being shifted to scalable architectures like Cloud and peerto-peer (P2P) models. In this paper, we consider the P2P model as a fully distributed, scalable system different from centralized coordinated systems in Cloud and Grid systems. A P2P system is composed of peer processes (peers). Here, applications are realized by activities of peers and cooperations among multiple peers. In P2P systems, since there is no centralized coordination, each peer has to obtain

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... n about other peers by itself. In the group cooperation, each group member peer has to be trustworthy so that malicious behavior of a member peer cannot effect overall outcome of the whole group. Here, it is important to consider the trustworthiness of each group member as a base of an agreement procedure in the distributed environment. The goal of a group and the way to archive the goal are decided by the group members. During the agreement procedure, opinions of member peers have to be collected in a group. Malicious and unexpected behaviors of member peers can negatively effect the output of a group. Hence, it is significant to discuss how to compose a group only by including more trustworthy peers. In this paper, by taking advantage of the trustworthiness concept of each peer, we propose a novel approach to composing a trustworthy group in the distributed agreement protocols.