 The MODS record has been designed to carry key data elements from the MARC record but does not define all of the MARC fields and does not use the field and subfield tagging from the MARC standard.There are data elements in MODS that are not compatible with the MARC record so there is some loss translating from MARC to MODS and from MODS to MARC.There is no commitment on the part of the Library of Congress to maintain compatibility between the two metadata formats beyond what is convenient to the community of MODS users.