  The Shintani-Tanaka model is a glass-forming system whose constituents
interact via anisotropic potential depending on the angle of a unit vector
carried by each particle. The decay of time-correlation functions of the unit
vectors exhibits the characteristics of generic relaxation functions during
glass transitions. In particular it exhibits a 'stretched exponential' form,
with the stretching index beta depending strongly on the temperature. We
construct a quantitative theory of this correlation function by analyzing all
the physical processes that contribute to it, separating a rotational from a
translational decay channel. Interestingly, the separate decay function of each
of these processes is temperature independent. Taken together with
temperature-dependent weights determined a-priori by statistical mechanics one
generates the observed correlation function in quantitative agreement with
simulations at different temperatures. This underlines the danger of concluding
anything about glassy relaxation functions without detailed physical scrutiny.
