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";