The design of the data warehouse back-stage has always been strenuous work, due to the inherent amount of complexity of this environment and the technical detail into which the designer must delve, in order to deliver the final design [6]. The task of the designer involves (a) the tracing of the existing data sources and the understanding of their hidden semantics, as well as (b) the design of a workflow that extracts data from these sources, cleans any inconsistencies they may have, transforms them in a suitable format and finally loads them into the target warehouse. The designer is aided by a conceptual model in order to complete the former task and a logical model in order to construct the latter. Also, a method that acts as a “bridge” that transforms the conceptual design to the logical one is also necessary.