Database: academic_minus_1_2
Question: return me the number of papers in PVLDB in " University of Michigan " .
SQL: select count ( distinct t3.title ) from organization_author as t1 join writes as t2 on t1.aid = t2.aid join publication as t3 on t2.pid = t3.pid join journal as t4 on t3.jid = t4.jid where t4.name = 'pvldb' and t1.name_organization = 'university of michigan' ;