Database: academic
Question: return me the number of papers in PVLDB in " University of Michigan " .
SQL:
SELECT COUNT ( DISTINCT t5.title ) FROM organization AS t2 JOIN author AS t1 ON t2.oid  =  t1.oid JOIN writes AS t4 ON t4.aid  =  t1.aid JOIN publication AS t5 ON t4.pid  =  t5.pid JOIN journal AS t3 ON t5.jid  =  t3.jid WHERE t3.name  =  "PVLDB" AND t2.name  =  "University of Michigan";