return me the number of the authors who have more than 10 papers containing keyword " Relational Database " . 
return authors ;return papers of  #1 ;return keywords in #2 ;return #2 where #3 contain Relational Database ;return number of  #4 for each  #1 ;return #1 where #5 is  higher than 10 ;return number of  #6
['select', 'project', 'project', 'comparative', 'group', 'comparative', 'aggregate']