code: def _build_graph(self, tags):
          
          graph = SimpleGraph()
          for tag_index in xrange(len(tags)):
              for entity_index in xrange(len(tags[tag_index].get('entities'))):
                  a_entity_name = graph_key_from_tag(tags[tag_index], entity_index)
                  tokens = self.tokenizer.tokenize(tags[tag_index].get('entities', [])[entity_index].get('match'))
                  for tag in tags[tag_index + 1:]:
                      start_token = tag.get('start_token')
                      if start_token >= tags[tag_index].get('start_token') + len(tokens):
                          for b_entity_index in xrange(len(tag.get('entities'))):
                              b_entity_name = graph_key_from_tag(tag, b_entity_index)
                              graph.add_edge(a_entity_name, b_entity_name)
  
          return graph
docs: Builds a graph from the entities included in the tags.
          Note this is used internally.
  
          Args:
              tags (list): A list of the tags to include in graph
  
          Returns:
              graph : this is the resulting graph of the tagged entities.