Final answer:
Schema-altering commands are classified as Data Definition Language (DDL) commands, which are used to create, alter, and drop database structures.
Step-by-step explanation:
Schema-altering commands are known as Data Definition Language (DDL) commands. The DDL is a subset of SQL that is used for creating and modifying the structure of database objects such as tables, indexes, and users. Commands in DDL include CREATE, ALTER, and DROP, which respectively allow you to create a new database object, modify an existing one, or delete one.