public class FreeVariableModelAnalysis
An analysis that traverses a model to determine all the free variables
in a hierarchical model. The free variables in a model are defined to
be the set of identifiers that are referenced by the model, but are
not defined in the model. The free variables must be assigned values
for the model to be executable.
This class traverses the model, but it not read synchronized on the
model, therefore its caller should be.
Analyze the given model to return a set of names which must
be defined externally for the model to be completely specified.
In addition, store the intermediate results for contained actors
so they can be retrieved by the getFreeVariables() method.