1. A method of migrating business data from a source system to an extensible destination system, the method comprising: at a computer, examining a structural definition of the extensible destination system, wherein the examining the structural definition of the extensible destination system includes accessing metadata related to the extensible destination system; synchronizing a structure of an intermediate database system with the extensible destination system, wherein the intermediate database system includes an entity extension table and an entity base table, the entity extension table and the entity base table are stored in a computer readable storage medium, wherein the synchronizing is performed prior to receiving source data, wherein the entity extension table is populated based upon an extension in the extensible destination system, the entity extension table exists only for destination extensible system entities that are customizable; collecting the source data from the source system and populating the synchronized structure of intermediate database system with the source data; specifying whether an attribute is used to define relationships between entities, whether the attribute should be migrated and migration status of the attribute; setting how many records from the entities are to be imported into the destination system when a migration tool is executed; specifying order in which the entities are migrated to preserve dependencies; migrating the source data from the intermediate database system to the extensible destination system according to migration overhead information, the migrating follows the order specified in the attribute, wherein the migration overhead information includes user-configurable, and an EntityMigrationInfo table and wherein the EntityMigrationInfo table specifies information about migration for each entity to be migrated.