  In this paper a duality between the d=2 Wen-plaquette model in a transverse
field and the d=1 Ising model in a transverse field is used to learn the nature
of the quantum phase transition (QPT) between a spin-polarized phase and a
topological ordered state with the string-net condensation. The QPT is not
induced by spontaneous symmetry breaking and there are no conventional
Landau-type local order parameters. Instead the string-like non-local order
parameters are introduced to describe the QPT. In particular, the duality
character between the open-string and closed string for the QPT are explored.
