Literature is all the carriers to record knowledge. Specifically, literature is a combination of words, symbols, images, audio and so on that record knowledge and information on a certain material carrier. From this definition, we can see that literature has three basic attributes, namely, knowledge, record and materiality. It has the functions of storing knowledge, transmitting and exchanging information.
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. Zero-order literature This is a special form of information source.
It mainly includes two aspects:
First, the knowledge information before the formation of literature, that is, the knowledge information that has not been recorded and has not formed written materials, is the non-documentary intellectual information of people's oral conversation and direct action on human sensory organs;
Second, the original documents that have not been 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 internal use.
Books and periodicals that cannot be obtained through open and regular ordering channels. 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.