1. A computer system for manipulating data in an object relational source database, the source database having data tables and a defined table type hierarchy with an associated tree structure, the system comprising, means for transforming data from the source database into a flat file data transfer file, comprising rows and columns, the means for transforming the source database comprising means for traversing the tree structure of the table type hierarchy using a tree traversal order, means for defining the columns in the data transfer file to correspond to the type definitions in the table type hierarchy for the source database, the means for defining the columns further comprising means for defining subcolumns corresponding to attributes defined in a respective type definition for a given column, the means for defining the columns further comprising means for defining a type identifier column corresponding to a type identifier determined during the traversal of the tree structure, the type identifier column values corresponding to defined types in the table type hierarchy and determined by the tree traversal order, the means for transforming data from the source database into the data transfer file further comprising means for copying rows of data from the tables in the source database into the data transfer file, each row in the data transfer file having a type identifier column value corresponding to the table in the table type hierarchy of the source database which is the source of the data in the row in the data transfer file.