This letter presents a new methodology for determining the compatibili
ty coefficients required for performing graph matching by probabilisti
c relaxation. The adopted framework is Bayesian and commences by speci
fying the effects of segmentation errors in corrupting the connectivit
y structure or topology of the graphs under match. This model of relat
ional constraint corruption leads to a pattern of compatibility coeffi
cients that is completely determined by the global topological propert
ies of the graphs under match. We illustrate the application of this n
ew theory in two graph matching applications. The first of these is co
ncerned with exploiting constraints provided by edges. Here the compat
ibility coefficient for consistent edges is equal to the inverse edge-
density. Our second illustration extends the compatibility model to th
e level of graph faces; the required coefficients are again parameter-
free. We provide experimental validation of our method in the matching
of aerial images. Here we demonstrate that the theoretical values of
our compatibility coefficients are close to their experimentally optim
al values.