Hierarchical graph representations for nested document structures

Extend the two-relation spatial graph representation used by Fragment to hierarchical graph formulations that can represent nested or deeply hierarchical document structures, such as nested table cells.

Background

Fragment represents structured documents as typed relational graphs whose edges encode spatial relations such as “below” and “right-of.” This representation is designed for Manhattan-style layouts and supports the Architect’s structural generation and the Builder’s attribute realization.

The paper explicitly identifies a limitation for documents containing nested or deeply hierarchical structures, noting that the current spatial edge types provide limited representational capacity in such settings. Developing a hierarchical graph formulation is therefore left as an unresolved direction for more expressive document generation and editing.