Suppose that a data warehouse consists of the three dimensions time, doctor and patient, and the two measures count and charge where charge is the fee that a doctor charges a patient for a visit. a. Enumerate three classes of schemas that are popularly used for modeling data warehouses. ( 3 Points) b. Draw a schema diagram for the above data warehouse using one of the schema classes listed in (a). (3 Points) c. Starting with the base cuboid [day, doctor, patient] what specific OLAP operations should be performed in order to list the total fee collected by each doctor in 2004 ? (2 Points) d. To obtain the same list, write an SQL query assuming the dates are stored in relational database with the schema fee (day,month,year,doctor, hospital,patient,charge,count). (2 Points)