A higraph is a diagramming object that formalizes relations into a visual structure, it was developed by David Harel

David Harel

David Harel is a professor of computer science at the Weizmann Institute of Science in Israel. Born in London, England, he was Dean of the Faculty of Mathematics and Computer Science at the institute for seven years.-Biography:...

 in 1988. Higraphs extend mathematical graphs

Graph (mathematics)

In mathematics, a graph is an abstract representation of a set of objects where some pairs of the objects are connected by links. The interconnected objects are represented by mathematical abstractions called vertices, and the links that connect some pairs of vertices are called edges...

 by including notions of depth and orthogonality

Orthogonality

Orthogonality occurs when two things can vary independently, they are uncorrelated, or they are perpendicular.-Mathematics:In mathematics, two vectors are orthogonal if they are perpendicular, i.e., they form a right angle...

. 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

Knowledge representation

Knowledge representation is an area of artificial intelligence research aimed at representing knowledge in symbols to facilitate inferencing from those knowledge elements, creating new elements of knowledge...

, and the behavioral specification of complex concurrent systems using the higraph-based language of statecharts.

Higraphs are widely used in industrial applications like UML

Unified Modeling Language

Unified Modeling Language is a standardized general-purpose modeling language in the field of object-oriented software engineering. The standard is managed, and was created, by the Object Management Group...

. Recently they have been used by philosophers to formally study the use of diagrams in mathematical proof

Mathematical proof

In mathematics, a proof is a convincing demonstration that some mathematical statement is necessarily true. Proofs are obtained from deductive reasoning, rather than from inductive or empirical arguments. That is, a proof must demonstrate that a statement is true in all cases, without a single...

s and reasoning.