Database: scholar
Question: When did Michael Stonebraker publish his GIS Database paper ?
SQL:
SELECT DISTINCT t3.year FROM paperkeyphrase AS t2 JOIN keyphrase AS t5 ON t2.keyphraseid  =  t5.keyphraseid JOIN paper AS t3 ON t3.paperid  =  t2.paperid JOIN writes AS t4 ON t4.paperid  =  t3.paperid JOIN author AS t1 ON t4.authorid  =  t1.authorid WHERE t1.authorname  =  "Michael Stonebraker" AND t5.keyphrasename  =  "GIS Database";