1. A method for mapping multiword expressions to identifiers using finite-state networks, comprising: encoding each of a plurality of multiword expressions into a regular expression; each regular expression encoding a base form common to a plurality of derivative forms defined by ones of the multiword expressions; compiling with factorization each of the plurality of regular expressions into a set of finite-state networks; performing a union of the finite-state networks in the set of finite-state networks to define a multiword finite-state network and a set of subnets; traversing the multiword finite-state network and the set of subnets to identify a path corresponding to one of the plurality of multiword expressions; wherein said traversing accounts for only transitions originating from the multiword finite-state network to ascertain a path number identifying a base form of the one of the plurality of multiword expressions.