Returns the span object of the term
        @rtype: List
        @return: the term span as list of wf ids

def get_span_ids(self):
        """
        Returns the span object of the term
        @rtype: List
        @return: the term span as list of wf ids
        """
        node_span = self.node.find('span')
        if node_span is not None:
            mySpan = Cspan(node_span)
            span_ids = mySpan.get_span_ids()
            return span_ids
        else:
            return []