###HUMAN: return me the number of papers in VLDB conference in ' University of Michigan ' ., ###ASSISTANT: SELECT COUNT(DISTINCT (publication.title)) FROM author, conference, organization, publication, writes WHERE conference.name = 'VLDB' AND organization.name = 'University of Michigan' AND organization.oid = author.oid AND publication.cid = conference.cid AND writes.aid = author.aid AND writes.pid = publication.pid