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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 dump_graph(self):
 """Dump a key-only representation of the schema to a dictionary. Every known relation is a key with a value of a list of keys it is referenced by. """

        # we have to hold the lock for the entire dump, if other threads modify
        # self.relations or any cache entry's referenced_by during iteration
        # it's a runtime error!
        with self.lock:
            return {
                dot_separated(k): v.dump_graph_entry()
                for k, v in self.relations.items()
            }