UML artifacts constitute a key (but often neglected) asset supporting the comprehension of a system. Design documents “bind” developers in implementation phases and close the loop as documentation of the implemented system itself. Nevertheless, the intended system (design), its current version (implementation), and its documentation, naturally tend to drift apart, negatively impacting the usefulness of UML diagrams contained in such artifacts.

We present a novel approach to capture and understand the Design-Implementation-Documentation (DID) drift. We connect UML references in human-readable text-based UML formats (e.g., PlantUML) to the corresponding source code entities (e.g., Java classes), implementing novel metrics to capture the UML coverage of the system. We analyze project and file coverage evolution across releases and commits, with overall, method-level, and attribute-level detailedness, showing how they support DID drift analysis. We present interesting case studies exemplifying how through Drifter, the visual exploration tool we developed to validate our approach, we identify DID drift and possible ways to tackle it in the future.