def _build_graph(self, tags):
        """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.

        """
        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
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.