1. A method for mapping relationships in a database, comprising: generating a directed schema graph for the database; grouping samples of records within tables of the directed schema graph into clusters, wherein said grouping includes approximating classes for said tables indicative of at least one of a table-reach equivalent class and a join-path equivalent class; based on the classes, identifying cluster pairs, wherein a cluster pair represents a join relationship between clusters in two tables of the database; generating a first mapping of the cluster pairs, wherein the cluster pairs are weighted according to a number of associated records; and storing the first mapping in a first storage device.