Hypergraph

A mathematical structure that generalises both trees and graphs by allowing edges (called hyperedges) to connect any number of nodes rather than being limited to exactly two. In the context of accessible graphical representations, hypergraphs are used to model the visual structure of charts and diagrams in a way that captures both hierarchical relationships (parent-child containment) and adjacent relationships (sibling connections) simultaneously. Unlike trees, hypergraph nodes can have multiple parents, preserving overlapping groupings without requiring node duplication. Unlike graphs, hypergraphs maintain a consistent relationship between hierarchy and adjacency: nodes are neighbours if and only if they share a parent. This makes hypergraphs well-suited for encoding the perceptual structure of complex visual representations for screen reader navigation.