Allocation of copies of a file in an information network

We consider a mathematical model of an information network of n nodes, some of which contain copies of a given data file. Within this network, every node is able to communicate with every other node over communication links (a process which may entail routing through intermediate nodes). In particular, we are concerned with transactions with the multiply-located file. Such transactions fall into one of two classes: (1) query traffic between a node and the file, and (2) update traffic. An update message is assumed to be transmitted to every copy of the file, whereas a query is communicated only to a single copy.