Nowadays, typical software and system engineering projects in various industrial sectors (automotive, telecommunication, etc.) involve hundreds of developers using quite a number of different tools. Thus, the data of a project as a whole is distributed over these tools. Therefore, it is necessary to make the relationships of different tool data repositories visible and keep them consistent with each other. This still is a nightmare due to the lack of domainspecific adaptable tool and data integration solutions which support maintenance of traceability links, semi-automatic consistency checking as well as incremental update propagation. Currently used solutions are usually hand-coded one-way transformations between pairs of tools only. In this article we propose a new rule-based approach that allows for the declarative specification of data integration rules concerning multiple data repositories. Hence, we call our approach "Multi Document Integration". It generalizes the formalism of triple graph grammars and replaces the underlying data structure of directed graphs by the more general data structure of MOF-compliant meta models. Our integration rule specifications are translated into JMI-compliant Java code which is used for various purposes by a tool integration framework. As a result we give an answer to OMG's request for proposals for a MOF-compliant "queries, views, and transformation" approach from the "model driven application development" (MDA) field.