It is suggested to use the single letter "A" as the document type identification of precipitated documents in monographs and papers. For other unspecified item types, it is recommended to use the single letter "z".
For the citation of electronic documents such as database, computer program and bulletin board system, it is suggested to use the following letters as identifiers: database DB, computer program CP and electronic bulletin EB.
The carrier types of electronic documents and their identification. For electronic documents with non-paper carriers, when they are cited as references, the carrier type should be indicated in the reference type identification. The fOLlowing signs are suggested: magnetic) MT' disk) DK' CD' online network (online) ol.