3 Tier Architecture
A formal, consolidated, corporate data warehouse for Business Intelligence implementations can guarantee a one version of the truth, the same information from different points of view for anyone in the organization. This is the main reason to add an additional layer to previous design.
By incorporating the datawarehouse layer, it is minimized data and process duplication efforts, all resources are utilized at optimum performance, the company obtains one version of the truth and increasing the confidence over BI implementation. Plus, the data marts maintenance is improved and can´t affect overall Business Intelligence implementation and performance, because all datamarts still isolated from another ones.