1. data definition: DBMS provides data definition language (DDL) for users to define the three-level schema structure, secondary image, integrity constraints and confidentiality constraints of the database. DDL is mainly used to establish and modify the database structure. The library structure described by DDL only gives the framework of the database, and the framework information of the database is stored in the data dictionary.

2. Data manipulation: DBMS provides data manipulation language (DML) for users to add, delete, update and query data.

3. Operation management of database: The operation management function of database is the operation control and management function of DBMS, including concurrency control, security check and access restriction control, integrity check and execution, organization and management of running logs, transaction management and automatic recovery, that is, to ensure the atomicity of transactions. These functions ensure the normal operation of the database system.

4. Data organization, storage and management: DBMS should classify, organize, store and manage all kinds of data, including data dictionary, user data and access paths. , and need to determine what file structure and access methods are used to organize these data at the storage level, and how to realize the connection between the data. The basic goal of data organization and storage is to improve the utilization rate of storage space and choose appropriate access methods to improve access efficiency.