The specificity is in the XML file, but only implicitly. In the XML file, each GO term has attributes "nabove" and "nbelow", where "nabove" is the number of parent GO terms between the term in question and the root term, and "nbelow" is the number of GO terms that have the term in question as a parent. The specificity is just
specificity = (nabove / (nabove + nbelow)) * (100)