A higraph is a diagramming object that formalizes relations into a visual structure, it was developed by David Harel in 1988. Higraphs extend mathematical graphs by including notions of depth and orthogonality. In particular, nodes in a higraph can contain other nodes inside them, creating a hierarchy. The idea was initially developed for applications to databases, knowledge representation, and the behavioral specification of complex concurrent systems using the higraph-based language of statecharts.
- Harel, D. (1988), On Visual Formalisms, Communications of the ACM, Volume 31, Number 5
- Grossman, O., Harel, D. (1997), On the Algorithmics of Higraphs, Technical Report, Rehovot, Israel