Assuming a desired minimum QoS (output rate) to be Rmin, for a given data stream management system, what is the bound on the number of data streams (maximum possible number of streams to be supported)? Adding new data stream means accepting new queries to the system, which means an increase in the cost of the computational network. Assuming that the cost of the computation network is a function of the number of streams n, that is C=f(n), then n is governed by the rule:

However, the relation between C and n (i.e. f) is not a simple one, that it might not be computationally feasible to calculate f^-1. So, to work around this problem, one can calculate an average query cost, and thus, one can base the bound based on this average query cost. Say the average query cost is Cavg then