Because there are many kinds of documents, each has its own characteristics, and the information content recorded by different types of documents also has its own emphasis, therefore, it will be of great help to further do a good job in document retrieval to understand the levels, types and characteristics of documents first.
According to the difference of knowledge transfer, information quality and quantity and processing level, documents are divided into four levels, which are called zero documents, first-class documents, second-class documents and third-class documents.
1 .0 document This is a special form of information source, which mainly includes two aspects: one is the knowledge information before the document is formed, that is, it is the oral conversation of people and the non-document information that directly acts on people's sensory organs; Second, the original documents that have not been publicly published in the society, or various books and periodicals that have not been officially published, such as letters, manuscripts, records, notes, etc., also include some books and periodicals that are used internally and cannot be obtained through public formal ordering. Zero-order documents are generally obtained by oral conversation, visiting exhibitions and attending reports, which not only has certain value in content, but also can make up for the time-consuming shortcomings of general public documents from the objective formation of information to public dissemination. 2. Documents This is a document produced by people directly according to their practical experience in production, scientific research and social activities. It is also often called the original document (or a kind of document), and its recorded knowledge and information are novel, specific and detailed. Primary literature is the largest, most diverse, most widely used and most influential literature in the whole literature system, such as periodical papers, patent documents, scientific reports, conference proceedings, dissertations and so on. These documents are innovative, practical and academic, which are the main basis for comparative analysis of documents in sci-tech novelty retrieval.
3. Second-level documents Second-level documents, also known as second-level documents, sort out, concentrate and refine a large number of scattered and disorderly first-level documents, arrange and store them according to a certain logical order and scientific system, and systematize them for retrieval and utilization. Its main types are catalog, index and abstract. The secondary literature is obviously collectible, systematic and retrievable. It collects not the original literature itself, but the clues of the original literature within a specific range. Its importance lies in greatly reducing the time spent searching a document. Secondary literature is the main tool used to retrieve literature in novelty retrieval.
4. Third-level documents Third-level documents, also known as third-level documents, are documents compiled by selecting a large number of related documents through comprehensive analysis and research. Usually, it is formed by collecting a large number of relevant documents around a certain topic through secondary literature retrieval and deeply processing its contents. There are reviews, comments, comments, progress, trends and so on. These documents comment, summarize and predict the development trend of existing achievements, which has high practical value. In the novelty retrieval work, we can make full use of the review literature reflecting the research trends in a certain field, and understand its research history, development trends and level in a short time, so as to more accurately grasp the technical background of the items to be retrieved and grasp the novelty retrieval points.
In short, from zero-level documents, first-level documents, second-level documents to third-level documents, it is a different level processing process of knowledge information from dispersion to concentration, from disorder to order, and from erudition to refinement. The quality and quantity of information they contain are different, and they play different roles in improving people's knowledge structure. The zero-level and first-level documents are the most basic information sources and the main objects of document information retrieval and utilization; Secondary literature is a centralized refining and sorting of literature and a tool for literature information retrieval; The three documents are the results of comprehensive analysis and processing of scattered zero documents, first-level documents and second-level documents according to the categories of topics or knowledge. They are highly concentrated literature information, which is not only the object of literature information retrieval and utilization, but also the tool of literature information retrieval.