複選題
20. The ANSI/SPARC has established a three-level architecture for a DBMS: conceptual, external, and internal. Which of the following is true?
(A) The conceptual level defines the low-level access methods and how bytes are transferred.
(B) The conceptual level interacts directly with the users.
(C) The internal level determines where data is actually stored on the storage devices.
(D) The external level interacts directly with the hardware. The data model is defined on this level, and the main functions of the DBMS are also on this level.
(E) The external level is an intermediary and frees users from dealing with the internal level.