Data Definition Language(DDL) Specification notation for defining the database schema Example: create table instructor( ID char(5), name varchar(20), dept name varchar(20), salary numeric(8,2)) DDL compiler generates a set of table templates stored in a data dictionary ■ Data dictionary contains metadata(i.e.,data about data) 。Database schema Integrity constraints Primary key(ID uniquely identifies instructors) 。Authorization Who can access what Database System Concepts-7th Edition 1.17 ©Silberscha乜，Korth and SudarshanDatabase System Concepts - 7 1.17 ©Silberschatz, Korth and Sudarshan th Edition Data Definition Language (DDL) ▪ Specification notation for defining the database schema Example: create table instructor ( ID char(5), name varchar(20), dept_name varchar(20), salary numeric(8,2)) ▪ DDL compiler generates a set of table templates stored in a data dictionary ▪ Data dictionary contains metadata (i.e., data about data) • Database schema • Integrity constraints ▪ Primary key (ID uniquely identifies instructors) • Authorization ▪ Who can access what