Supporting and applying the UML conceptual framework

The Unified Modelling Language (UML) ostensibly assumes a four level (meta) modelling framework, both for its definition and for the conceptual context in which its users operate. In practice, however, it is still dominated by the traditional two level (model + data) view of object modelling and neither supports nor applies the four level framework properly. This not only diminishes the clarity of the UML semantics, but also complicates the task of those users who do wish to fully embrace a multi-level approach. After outlining the characteristics of the intended conceptual framework, and the problems resulting from the UML's current two-level bias, this paper presents three simple enhancements to the UML which provide the required expressive power for multi-level modelling. The paper then goes on to discuss issues in the application of the conceptual framework within the UML's own definition.