The paper presents a framework for evaluating the comparative use of system resources in message communication, building on the framework of Locative Temporal Logic (M.J. Wieczorek, 1994) by adding "costs" either to the underlying graph representing the communications network of the system in question, or to the messages/actions of the system. This is intended to aid the specification of distributed systems which have to communicate many different types of data, for example multimedia distributed systems. This framework is intended to define requirements. With further refinement of the specifications, the architecture and then an implementation could be derived from the specifications. The specifications can be validated either by simulation with an appropriate tool or by formal proof of correctness of the specifications. The specifications are derived from the description of an application (even a very abstract specification of an application).