1. A method comprising producing plural response descriptions that describe responses of nodes of a distributed system, said plural response descriptions being produced by applying symbolic evaluation to plural node behavior descriptions of the nodes, the operation of the nodes being described by respective ones of the node behavior descriptions; combining at least the plural response descriptions so as to arrive at a description of potential responses of the distributed system; and in response to at least one input requirement that is input from a client, outputting a description of at least one potential response of the distributed system.