The shift of development effort onto the model level, as postulated by MDA, provides an opportunity for establishing a set of modelling constructs that is more intuitive and homogeneous than its platform-specific counterparts. In this paper we confront UML with the needs specific for data-intensive applications and propose a seamlessly integrated platform-independent language with powerful querying capability, which would allow specifying a complete application behaviour. The proposal is aimed at high level of compliance with existing modelling standards – as such it is based on UML behavioural elements and on OCL for expressions. We present the motivation behind this approach, discuss the challenges implied by it, and indicate the role of the model runtime implementation.