The literature review belongs to the third literature
1. Primary document: that is, original document, usually refers to the author's original creation. The content recorded in this type of literature is specific, systematic, detailed, innovative and creative, and is the main object of literature retrieval. Monographs, journal articles, dissertations, research reports, conference papers, patent specifications, etc. are all primary documents.
2． Secondary literature: generic search tool. It is made by compressing primary documents, collecting, sorting, processing and compiling scattered and disordered primary documents. Because it provides clues and convenience for finding and utilizing primary documents, it is regarded as the main tool and method for document retrieval. Bibliography, table of contents, index, abstract, etc. are secondary documents.
3. Tertiary documents: Generally based on the extensive use of secondary documents, a large number of primary documents are selected, read, researched, and condensed and refined. The three-dimensional literature may comment on the results and progress achieved, or predict development trends, so that readers can understand the current research level and dynamics. Therefore, it is considered a high-level intelligence. Yearbooks, progress, reviews, reviews, etc. are all three types of documents.