This International Standard specifies a data struc-ture known as the SGML Document Interchange Format (SDIF). SDIF enables a document conform-ing to ISO 8879, which might be stored in several entities, to be packed into a data stream for interchange in a mannerthat will permit the recipient to reconstitute the separate entities.
SDIF also allows related documents to be included in the data stream, such as covering letters, trans-mittal forms, catalog cards, formatting procedures, or the "document profile" required by a document architecture.