4.1 State why, for the integration of multiple heterogeneous information sources, many companies in industry prefer theupdate-driven approach(which constructs and uses data warehouses), rather than the query-driven approach (which applies wrappers and integrators). Describe situations where the query-driven approach is preferable to the update-driven approach.
4.2 Briefly compare the following concepts. You may use an example to explain your point(s).
(a) Snowflake schema, fact constellation, starnet query model
(b) Data cleaning, data transformation, refresh
(c) Discovery-driven cube, multifeature cube, virtual warehouse
4.3 Suppose that a data warehouse consists of the three dimensions time, doctor, and patient, and the two measures ...