Locating replicas of a database on a network

We study the problem of locating replicas of a database on a network to minimize the communication cost. We first present extensions of the p-median theorem to prove that under two different measures of communication cost one can always optimally locate the replicas at the vertices (nodes) of the network. We briefly review that fact that the problem is NP-hard for general networks under either measure of communication cost, and we then provide efficient algorithms for solving the problem on tree networks for either of the two measures.