The main function of dbms is to provide data definition language to define the three-level schema structure of data, including schema, external schema and internal schema, and define the two-level image of schema/internal schema and external schema/schema, and define related constraints. Define user passwords and access rights to ensure database security, and define integrity rules to ensure correct semantics. Structured Query Language (SQL) provided by DBMS provides statements such as Create, Drop and Alter, which are used to create, delete and modify databases respectively.

Data operation function of database management system

DBMS provides DataManipulationLanguage (DML) to realize basic operations on the database, including retrieval, update (including insertion, modification and deletion) and so on. Therefore, the compiler or interpreter of DML should also be included in DBMS. There are two types of DML: one is autonomous or independent, and the other is interactive command language, which has simple grammar and can be used independently.

The other is the host type, which embeds the access statement into the database with high-level languages (such as Fortran, Pascal, C, etc.). ) and cannot be used alone. SQL is a DML. For example, SQL, a structured query language provided by DBMS, provides query statements (Select), Insert statements, update statements and delete statements, which can query, insert, modify and delete data records in the database respectively.