Which statement is not correct?

a. A data mart is a scaled-down version of a data warehouse aimed at meeting the information needs of a homogeneous small group of endusers such as a department or business unit (e.g., marketing, finance, logistics, HR, etc.).

b. Dependent data marts pull their data from a central data warehouse, whereas independent data marts are standalone systems drawing data directly from the operational systems, external sources, or a combination of both.

c. A virtual data warehouse (sometimes also called a federated database) or virtual data mart contains no physical data but provides a uniform and consolidated single point of access to a set of underlying physical data stores.

d. A key advantage of virtualization is that it requires no extra processing capacity from the underlying (operational) data stores.