According to GB3469-83 "Document Types and Document Carrier Codes", it is identified with a single letter: M- monograph (including historical records in ancient books) c- anthology n- newspaper article J- journal article d- dissertation r- research report s- standard p- patent a- monograph, and documents deposited in the anthology Z- other unspecified document types-electronic document types are identified with two letters: d. Title [J] Volume (issue): Page 2. Monograph author. Title [m]. Version (first edition not recorded). Place of publication: publisher, year of publication: page 3. The author of the program. Title [c]. Edit. Title of the paper, place of publication: publisher, year of publication: page 4. Author of the paper. Title [D] Save the location. Save unit. The fifth year. Title of the patent document [P]. Country. Patent number. Publication date 6. Standard number. Standard name 7. Newspaper writer. Title. Newspaper name. Publication date (version) 8. Author of electronic document. Title [Identification of electronic documents and carrier types]. Source of the document, date II. Document type and its identification 1. According to GB3469, various commonly used documents can be identified as follows: ① periodical [J] ② monograph [M] ③ thesis [C] ④ dissertation [D] ⑥ patent [P] ⑥ standard [S] ⑥ newspaper [N] ⑧ technical report [R] 2. The carrier type of an electronic document is identified by two letters. The details are as follows: ① magnetic tape [MT] ② disk [DK] ③ optical disk [CD] ④ online network [OL] 3. The method of identifying the reference type of electronic document carrier is [document type identification/carrier type identification]. For example, ① online database [DB/OL] ② tape database [DB/MT] ③ CD books [M/CD] ④ disk.