Nowadays, the growth of virtual environments such as virtual organizations, social networks, and ubiquitous computing, has led to the adoption of trust concept. One of the methods of making trust in such environments is to use a long-term relationship with a trusted partner. The main problem of this kind of trust, which is based on personal experiences, is its limited domain. Moreover, both parties of such trust relationship will face big problems of collecting data and forming reasonable and reliable beliefs. Considering the concept of "group" in modeling trust is a way to overcome the above mentioned problems. Since, group-based trust is more suited with the nature of trust in new virtual environments. In this paper, a new trust model called "GTrust" is proposed in which trust is considered as a collective and shared feature of all group members. Therefore, group membership is used as the judgment criteria regarding a person's expected behavior and how he can be a trustee. GTrust is based on Metagraphs which are graphical data structures for representing a collection of directed set-to-set mappings. We show that by using GTrust, large trust spaces between unknown individuals can be shaped effectively. The proposed model not only offers a better description of human sense of trust when considering communities, but also provides the setting for evaluating the trust of individuals whom we do not know, and therefore provides an extended evaluation domain.
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