The design of data warehouse is a very relevant issue in supporting the management decisional processes and data analysis. While the design and maintenance of data warehouses are dificult tasks, enterprise managements are increasingly asking for tools capable to support designers in all the activities involving data warehouse construction. In this context it is mandatory to provide designers with the capability to incrementally define data warehouse components. In this paper we propose a conceptual model, called Multidimensional Fact Network (MFN), allowing to incrementally define data marts and a toolkit, called AURORA, based on MFN and providing a comprehensive set of data warehouse design tools.