The characteristics of zero-order documents are objectivity, fragmentation and immaturity. Including: letters, manuscripts, meeting minutes, notes, etc.
The characteristics of a literary work: first, originality; Second, the specific and detailed content; Third, the number is huge and difficult to find. Including: periodical papers, patent documents, scientific and technological reports, conference proceedings, dissertations, etc.
Characteristics of secondary literature: 1. Concentration, 2. Collectivity and 3. Systematize. Including: bibliography, title record, introduction, abstract and other retrieval tools.
The characteristics of the three documents are centralization, guidance, pertinence and reference. Including: overview, thematic summary, annual summary of disciplines, progress report, data manual, dictionary, electronic encyclopedia, etc.