def grouped_mappings(self,id):
        """
        return all mappings for a node, grouped by ID prefix
        """
        g = self.get_xref_graph()
        m = {}
        for n in g.neighbors(id):
            [prefix, local] = n.split(':')
            if prefix not in m:
                m[prefix] = []
            m[prefix].append(n)
        return m
return all mappings for a node, grouped by ID prefix