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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 load_from_rdf_string(self, rdf_str):
 """Initialize given an RDF string representing the hierarchy." Parameters rdf_str : str An RDF string. """

        self.graph = rdflib.Graph()
        self.graph.parse(data=rdf_str, format='nt')
        self.initialize()