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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _post_process_yaml_data(self, fixture_data: Dict[str, Dict[str, Any]], relationship_columns: Set[str], ) -> Tuple[Dict[str, Dict[str, Any]], List[str]]: """ Convert and normalize identifier strings to Identifiers, as well as determine class relationships. """

        rv = {}
        relationships = set()
        if not fixture_data:
            return rv, relationships

        for identifier_id, data in fixture_data.items():
            new_data = {}
            for col_name, value in data.items():
                if col_name not in relationship_columns:
                    new_data[col_name] = value
                    continue

                identifiers = normalize_identifiers(value)
                if identifiers:
                    relationships.add(identifiers[0].class_name)

                if isinstance(value, str) and len(identifiers) <= 1:
                    new_data[col_name] = identifiers[0] if identifiers else None
                else:
                    new_data[col_name] = identifiers

            rv[identifier_id] = new_data
        return rv, list(relationships)