  Probabilistic transition system specifications using the rule format
ntmuft-ntmuxt provide structural operational semantics for Segala-type systems
and guarantee that probabilistic bisimilarity is a congruence. Probabilistic
bisimilarity is for many applications too sensitive to the exact probabilities
of transitions. Approximate bisimulation provides a robust semantics that is
stable with respect to implementation and measurement errors of probabilistic
behavior. We provide a general method to quantify how much a process combinator
expands the approximate bisimulation distance. As a direct application we
derive an appropriate rule format that guarantees compositionality with respect
to approximate bisimilarity. Moreover, we describe how specification formats
for non-standard compositionality requirements may be derived.
