According to Johnson [20], even when these large projects are successful, their usage rate is low, with less than 40% of implemented functions in use. This occurs because of two main problems. The first one is the lack of synchronization between the development team and end users of a DW (e.g., physicians, researchers or businessman). Due to the extended development time on large projects, the align- ment between user needs and the final solution implemented is adversely affected. The other problem is that the traditional process for DW construction does not allow rapid and partial deliveries of functional features. Usually, projects will only be available to end users after they have been fully implemented, which can take months or years. After these lengths of time, it is likely that their data will already be out of date and no longer relevant.
This paper addresses the following question: how can the complexity of DW development for integration of heterogeneous transactional information systems be reduced? To answer this question, we proposed methodological guidelines for construction of DW based on cycles of conceptual modeling and data analysis, to drive creation of a modular DW system. Trying to improve these guidelines through a real usage ex- perience, we have applied them in the Retrovirus Epidemiology Donor Study-II (REDS-II) project, reducing the DW development complextiey