Cost Graphs for Concurrent Calculi

We present a theory of cost of concurrent programs, which is an important measure to evaluate their quality. The basic idea is to assign each program a set of graphs which give derivation of a program argumented with cost information, then order two progra.m$\mathrm{s} $ by comparing these two sets. According to the ways of comparing these sets, various orderings which capture specific aspects of efficiency of concurrent programs arise. We show that the efficiency preorder presented by Arun-Kumar and Hennessy, is closely related with one of these orders, thus showing our theory is a conservative extension of their construction.