Ralph kimball proposed the bottum-up design approach of data warehouse. In bottom-up approach datamarts are created first. T datamarts are then integrated and a comprehensive data warehouse is created. As the datamarts are created first, business solutions can be answered quickly.
Bill Inmon proposed the top-down up design approach of data warehouse. In top-down approach complete data warehouse is created first and then the datamarts are derived from the data warehouse. As the datamarts are created from a single data warehouse, all the datamarts has consistent data. It is robust against business changes. The cost of the project is very high.