1. A method for computing paths through a data network that includes a subnetwork which introduces a subset intransitivity constraint on allowable paths through the data network, the method comprising: using an abstracted map of the network that includes network elements (NEs) and subnetwork elements (SNEs), with links between pairs of the NEs and the SNEs to construct a directed graph that compensates for the subset intransitivity; and applying a routing algorithm to compute paths from a start node to the other nodes of the directed graph.