from abc import ABC, abstractmethod
from typing import Iterable, Set


class Graph(ABC):
    @abstractmethod
    def get_column_identity(self, key: str) -> str:
        pass

    @abstractmethod
    def get_related_columns(self, key: str) -> Set[str]:
        pass

    @abstractmethod
    def iter_clusters(self) -> Iterable[Set[str]]:
        pass