Navigating Hierarchical Visual Diagrams in Complex Machine Modelling : Design and Evaluation of a Node-Based Interface for OpenPLX Models

Designing visual interfaces for complex machine simulation models presents unique challenges, particularly in representing hierarchical structures and mechanical connections in a clear and accessible way. This is especially relevant in the context of OpenPLX, an open-source declarative modelling language developed for creating digital twins with integrated physics. This thesis applied a Design Thinking approach involving user interviews and iterative prototyping to explore how a node-based interface could enhance navigation and model understanding. Initial research revealed difficulties users face in navigating large text-based OpenPLX files and understanding complex component relationships. A core design decision was to represent mechanical connections not merely as lines, but as independent nodes containing their own parameters and internal structure, aiming for a more accurate reflection of mechanical reality. To manage visual complexity and aid navigation in large graphs, the design incorporated features such as collapsible node groups, predefined abstraction levels (overview, subsystems, full detail), and a focus mode to highlight relevant elements. Two navigation patterns were explored and prototyped: opening nodes in new tabs and expanding them in the same view, supported by aids like breadcrumbs and a minimap. User testing with four internal OpenPLX users provided validation and insights. Users easily understood the hierarchical structure. The concept of connections as nodes was generally well-received, though some preferred simpler visual representations. Abstraction levels and grouping/collapsing features were valued for complexity management. Breadcrumbs were praised for maintaining context. However, connection line colours caused confusion, and the feature to dim unrelated nodes was not immediately obvious. Collapsing nodes also raised a perception of altering model structure for one user. In conclusion, the project successfully identified and prototyped design strategies for a node-based interface in complex machine modelling, focusing on clear representation of hierarchy and connections, and effective navigation and complexity management. While the design patterns show internal validity and address key user needs, the reliability and external validity are limited by the small sample size of internal users, highlighting the need for broader validation.