There are several tables in the thesis database. What is the relationship between them? Four information tables: reader information table, book information table, borrowing information table and data flow table. Academic papers are the knowledge and scientific records of an academic subject with new scientific research achievements or innovative ideas in experiments, theories or observations; Or apply the known principles to the scientific summary of the new progress made in practice for reading, communication or discussion at academic conferences; Or published in academic journals; Or written documents for other purposes.