1. Primary documents, also known as original documents, generally refer to monographs, papers, investigation reports and other documents that directly record events, research achievements, new knowledge and new technologies. A Literature includes original literature such as monographs, papers, investigation reports and archival materials based on the author's own practice.

2. The secondary literature is to process the original literature to make it systematic and organized. Usually called retrieval literature, it generally includes title, bibliographic index, abstract and abstract. Secondary literature is reportable, collective and concise, which is the understanding of primary literature and the main component of retrieval tools.