With respect to database systems, which of the following statement(s) is (are) true?

a. A record layout shows the items stored in a file, including the type of data stored and both the order and length of the data fields.

b. The physical view of data is how people conceptually organize and understand the relationships among data items.

c. A DBMS allows users to query or update a database without knowing where data are actually stored.

d. The DML builds the data dictionary, creates the database, describes logical views for each user, and specifies security constraints.

e. The external-level schema is the organization-wide view of a database and lists all data elements and the relationships among them.