Trust and trustworthiness are significant measurements of a distributed sensing system or a heterogeneous network comprised of sources of information, knowledge, hardware and software. In an effort to design a unified trust model that can be made adaptable to changing application environments, we present fundamental features and rules extracted from literature pertaining to wireless sensor networks, social networks, e-commerce, mobile ad-hoc, peer-to-peer, and distributed network services. The design constraints are: it must (a) support a heterogeneous network, (b) obtain and evaluate multiple trustworthiness measures, (c) be carried out with computational ease without extensive computational power from the sensor network, and (d) be conceptually simple but have a firm basis in theory.