Preface is the beginning of a document or book, usually written by the author, with the purpose of introducing the background, purpose and writing motivation of the work to readers, and providing some key information and guidance to help readers better understand and read the follow-up content. The preface is generally long, which can include personal experience, research methods, theoretical framework and so on. Abstract is a brief overview of a document or paper, usually before the text, in order to provide readers with a quick overview of the full text. It is usually brief, including the research purpose, methods, main results and conclusions. The main function of the paper is to make readers quickly understand the core content of a document or paper, so as to decide whether it is necessary to read the full text further.