1. A network element (NE) comprising: a receiver configured to receive a path computation request; a path computation element (PCE) coupled to the receiver and configured to: compute a group of network paths through a network of NEs operating in a network stratum in response to the path computation request, wherein each network path comprises one or more physical links; and compute at least one constraint for each physical link; and an abstraction module coupled to the PCE and configured to: receive the computed network path set and constraints; compute one or more abstract links that describe the network path group; and compute a constraint for each abstract link based on the physical link constraints.