  Kinetically constrained spin models are known to exhibit dynamical behavior
mimicking that of glass forming systems. They are often understood as
coarse-grained models of glass formers, in terms of some "mobility" field. The
identity of this "mobility" field has remained elusive due to the lack of
coarse-graining procedures to obtain these models from a more microscopic point
of view. Here we exhibit a scheme to map the dynamics of a two-dimensional soft
disc glass former onto a kinetically constrained spin model, providing an
attempt at bridging these two approaches.
