A Unified Modelling Language without referential redundancy

The paper argues that, as a language for representing concrete problem domains, the quality of the UML is compromised by its many referentially redundant modelling constructs. A referential redundancy occurs when several modelling constructs or model elements refer to the same classes, things or properties in the problem domain. Referential redundancy compromises language and model quality because it hampers consistency checking, update reflection and reuse of model content between different diagrams or models. To alleviate this problem, the paper shows how the relevant parts of the UML can be reformulated using faceted metamodelling, so that referential redundancy is eliminated at the language level and potentially reduced at the model level. The discussion contrasts faceted metamodelling with conventional metamodelling using metaobjects, -properties and -relationships and argues that many of the referential redundancies in the UML are introduced by the conventional metamodelling approach used to define it.