Different trust and/or reputation models have arisen in the last few years. All of them have certain key processes in common such as scoring, ranking, rewarding, punishing or gathering behavioral information. However, there is not a standardization effort for these kinds of models. Such effort would be beneficial for distributed systems such as P2P, ad-hoc networks, multi-agent systems or Wireless Sensor Networks. In this paper we present a pre-standardization approach for trust and/or reputation models in distributed systems. A wide review of them has been carried out, extracting common properties and providing some pre-standardization recommendations. A global comparison has been done for the most relevant models against these conditions, and an interface proposal for trust and/or reputation models has been proposed.