Libra+: Compositional Interaction for Data Visualization

We present Libra+, a high-level conceptual model and library for interactive data visualization that supports the composition of primitive interactions into sophisticated ones. Libra+ formalizes interactions through a Trigger–Target–Feedback model, which specifies input events that initiate an interaction, the target on which it operates, and the resulting feedback. This model serves as a semantic bridge between high-level interaction intent and its modular, concrete implementation. To operationalize this approach, we define atomic instruments as reusable interaction units and introduce coordination strategies for composing them across graphical layers and views. By resolving input conflicts, supporting cross-layer synchronization, and enabling customizable feedback, Libra+ provides both a vocabulary for interaction design and a practical framework for building modular, extensible, and composable interactions for visualizations. We implement this model as an extension of Libra.js [32] and demonstrate that Libra+ can reproduce sophisticated interactive visualizations and generalize existing interactions to new contexts through a set of use cases. By enabling the parametrized composition of instruments, our unified interaction framework promotes modularity and extensibility in visualization interaction design.