returns a list of URIs and blanknodes that are not defined within
        the dataset. For example: schema:Person has an associated rdf:type
        then it is considered defined.

        args:
            data: a list of triples
            class_types: list of subjects that are defined in the dataset

def _get_non_defined(self, data, class_types):
        """
        returns a list of URIs and blanknodes that are not defined within
        the dataset. For example: schema:Person has an associated rdf:type
        then it is considered defined.

        args:
            data: a list of triples
            class_types: list of subjects that are defined in the dataset
        """
        subj_set = set([item[self.smap] for item in class_types])
        non_def_set = set([item[self.smap] for item in data])
        return list(non_def_set - subj_set)