The set of characteristics needed to define a resource is called a resource trait. Resource traits are taken as a parameter during service initialization in the am_resource_traits_t. Using the resource traits, the Policy Service constructs a resource graph for policy evaluation in which the relation between all resources in the system spans out like a tree from the root of the given resource. Thus, the service developer must provide the means to extract the root of the given resource. In a URL, the protocol://resource-host.domain:port portion represents the root.