For precipitated documents in monographs and papers, it is recommended to use the single letter "A" for document type identification; For other unspecified literature types, it is suggested to use the single letter "Z".
For the citation of electronic literature types such as databases, computer programs and bulletin board system, it is suggested to use the following two letters as identification:
The carrier type and identification of electronic documents
For electronic documents with non-paper carriers, when they are cited as references, the carrier type should be indicated in the reference type identification. This specification suggests using two letters to indicate the carrier type of electronic files: magnetic tape)-MT, magnetic disk)-DK, CD-ROM-CD, online)——OL, and indicating the reference type identification including the carrier type in the following format:
[File Type Identification/Carrier Type Identification]
Such as: [db/ol]-online database online.
A database on tape.
[m/CD]- CD monograph
[CP/DK]- Disk software (computer program on disk)
Online serial
[EB/ol]- Online bulletin board system.
Traditional literature with paper as the carrier does not need to indicate the carrier type when it is cited as a reference.