  CIF is a language designed for two purposes, namely as a specification
language for hybrid systems and as an interchange format for allowing model
transformations between other languages for hybrid systems. To facilitate the
top-down development of a hybrid system and also to be able to express models
more succinctly in the CIF formalism, we need a mechanism for stepwise
refinement. In this paper, we add the notion of hierarchy to a subset of the
CIF language, which we call hCIF. The semantic domain of the CIF formalism is a
hybrid transition system, constructed using structural operational semantics.
The goal of this paper is to present a semantics for hierarchy in such a way
that only the SOS rules for atomic entities in hCIF are redesigned in
comparison to CIF. Furthermore, to be able to reuse existing tools like
simulators of the CIF language, a procedure to eliminate hierarchy from an
automaton is given.
