Before comparing the content of two Oracle schemas, data compare performs a mapping of schema objects, i.e. tables and, optionally, views. By default, a table on one schema is mapped to a table on the other schema that has the same name. Depending on the comparison options, views and can also be mapped with each other. If you choose to compare specific tables or views, then data compare honors the manual mapping, compares only the selected objects and ignores the rest of the schema.
Once the object are mapped, data compare analyzes columns and chooses a suitable unique key that will be used to compare the data rows.
During this preparation phase you will be able to customize the object mapping, include and exclude certain tables and certain columns within those tables, choose comparison keys and define data filters to compare only subsets of rows.