  We examine the kinetics of surface diffusion-controlled, solid-state
dewetting by consideration of the retraction of the contact in a semi-infinite
solid thin film on a flat rigid substrate. The analysis is performed within the
framework of the Onsager variational principle applied to surface
diffusion-controlled morphology evolution. Based on this approach, we derive a
simple, reduced-order model to quantitatively analyse the power-law scaling of
the dewetting process. Using asymptotic analysis and numerical simulations for
the reduced-order model, we find that the retraction distance grows as the
$2/5$ power of time and the height of the ridge, adjacent to the contact, grows
as the $1/5$ power of time for late time. While the asymptotic analysis focuses
on late time and a relatively simple geometric model, the Onsager approach is
applicable to all times and descriptions of the morphology of arbitrary
complexity.
