i5/OS™ DDM supports access to a logical file by using the DDM alternate index file model.
A logical file allows access to the data records stored in a physical file by using an alternate index defined over the physical file. Only single format logical files can be accessed through i5/OS DDM. Logical files with select/omit logic can be accessed, but records that are inserted might not be retrievable if they are omitted by the select/omit logic.
An iSeries™ alternate index file can have fixed-length record (RECFIX) or variable-length record (RECVAR) for storage.
Once a non-iSeries source server opens a file on the iSeries target using variable-length record access, the iSeries target continues to send and receive variable-length records on all subsequent I/O operations.