The purpose of this paper is to propose a methodology for defining database navigation rules with the help of the XML language. This enables the introduction of the concept of the dynamic application server - a server that can be instantiated with the help of a relevant, "database-descriptive" XML document and acquire from it all the necessary knowledge for performing queries on the particular database. In order to support those ideas, the paper presents several hierarchical models: business application information model, database model and database navigation model. In the end, those models are integrated into a single, concrete model that eases the definition and creation of three-tier business applications, whose main characteristic is the easy adaptation to any legacy database.