Nowadays, the data warehouse is recognized as the essential component of decision support systems since it ensures the best response to the decision problems of different functional areas of an organization. However, the construction and design of the data warehouse remain a very complex task which is difficult to accomplish. This complexity is mainly due to the absence of conventional techniques and methods that are recognized in the field. Thus, the present paper identifies different rules for designing a data warehouse from relational data and introduces a new method that aims to automate this process using MDA techniques and XML.