Our project is combining UML with the B formal method for the domain of data intensive information systems. It consists in extracting a subset of UML concepts suitable for the analysis of such systems , producing derivation rules from UML diagrams to B specifications and developping a prototype support tool. A preliminary step is to precisely define the syntax and semantics of the required UML notations. This is achieved using a metamodelling technique. In this article we present the specialised metamodels, in UML and B notations, for structural (class diagrams) and behavioural (state transition and collaboration diagrams) elements. Then we outline how the formal metamodel is used in the development of the tool.