Contrast an operational database with a data warehouse. Which of the following statements is not true about this contrast?

Select one:

a. Operational databases are volatile, while data warehouses are non-volatile (that is, past data are not erased when new data are added).

b. The two are usually separated from each other in an organization, and ETL is usually necessary for data warehouses but not for operational databases.

c. An operational database contains summarized past (historical) data, while a data warehouse contains granular current data.

d. An operational database query allows to read and modify operations, while an OLAP query (used with a data warehouse) needs read only access of stored data.

e. An operational database supports concurrent processing of multiple transactions; thus, concurrency control and recovery mechanisms are required for operational databases to ensure robustness and consistency of the database but not required for data warehouses.