Information from source databases is retrieved and stored on a database storage system. Multiple point-in-time copies are obtained for each database. A source database may contain partitions comprising sets of database tables. A partition is imported into a virtual database created. The database storage system validates the partition before importing, by checking whether the partition includes database tables that refer to database tables outside the partition. A partition imported in a virtual database may be rewinded to an older state or refreshed to a more recent state. Multiple partitions may be included in a virtual database and the state of each partition modified independent of the state of the remaining virtual database including the other partitions. Multiple versions of the same partition corresponding to different points in time are incorporated in the same virtual database, thereby allowing a query to process different versions of the same database table.