Contents, indexes and abstracts belong to secondary literature.
Review, comment and comment belong to three documents.
Literature can be divided into first-class literature, second-class literature and third-class literature according to its content, nature and processing mode. Primary literature refers to the original literature created on the basis of the author's own research results, such as periodical papers, research reports, patent specifications, conference papers, etc. Secondary literature is a retrieval tool, such as bibliography, title, introduction, abstract and so on. The third generation literature comes first. Documents compiled after comprehensive analysis are usually called the results of "information research", such as reviews, thematic reviews, annual summaries of disciplines, progress reports, data manuals, etc. Similarly, information is divided into primary information, secondary information and tertiary information.
Original documents
(Primary document): refers to the document created or written by the author according to his own research results. No matter whether he refers to or quotes other people's works when creating, no matter what material form the document appears, it is a document. Most of the articles published in journals and papers published in scientific and technological conferences are a document.
The second article
(Secondary literature): refers to the products obtained by the literature workers after processing, refining and compressing the primary literature. It is a tool document edited, published and accumulated to facilitate the management and utilization of original documents. Search reference books and online search engines are typical secondary documents.
Three documents
Third-level literature: refers to the products of extensive and in-depth analysis and research on related first-level and second-level literature, such as encyclopedias and dictionaries.
Some researchers have added zero-order documents to the above classification, which refer to the original documents without any processing, such as experimental records, manuscripts, original audio recordings, original video recordings, conversation record, etc. Zero-level documents play an important role in the preservation of original documents, the verification of original data and the verification of original ideas (owners).