ignore class for jaxb schemagen generation

Question

I have two groups of classes. From the ones in group A I would like to generate an XML Schema using schemagen and the one's in group B I simply want to ignore with regard to the schema generation. How can I do that? I only annotated the classes in groupA jaxb related. When trying to generate the schema I get "does not have a no-arg default constructor" for the classes of group B.