Source information recorded on informal physical carriers without any processing is called zero-level information, such as letters, papers, notes, experimental records, meeting records, etc. This is a kind of sporadic, scattered and irregular information.
The carrier form of zero-level information is called zero-level literature, which has been gradually recognized and valued in recent 20 years. It has the characteristics of originality, novelty, dispersion and non-retrieval.
Different information carriers
Zero documents are usually letters, manuscripts, notes, experimental records, meeting records, etc.
Original documents usually include periodical papers, research reports, patent specifications, conference papers, dissertations, technical standards, etc. These documents are obviously innovative, practical and academic.
Secondary literature, such as bibliography, title record, introduction, abstract and other retrieval tools.
Review, thematic review, annual summary of disciplines, progress report and data manual.