This article explains how with the application of Agile and Lean principles on model-driven development, we will get an Agile approach for constructing the architecture of a new Market Server Capability (MSC)definition which will eliminate the duplication and inconsistency, while still maintaining a short implementation phase. The resulting architecture has a single modeling level, with merged PIM and PSMs. The model is designed by reverse engineering of the legacy code in a Test Driven Development fashion.