Nowadays an information exchange on XML such as B2B electronic commerce is spreading. Therefore the systematic and stable management mechanism for storing the exchanged information is needed. For this goal there are many research activities for connection between XML application and database. Accordingly, A unified modeling methodology need to store the XML file on the variety database. In this paper, we propose a unified design methodology for XML applications based on variety databases using UML. To this goal, first we introduce a XML modeling methodology to design W3C XML schema using UML and second we propose data modeling methodology for object-relational database schema, object oriented database an schema and relational database schema to store efficiently XML data in databases.