GraphML

GraphML is an XML-based file format for graphs. The GraphML file format results from the joint effort of the graph drawing community to define a common format for exchanging graph structure data. It uses an XML-based syntax and supports the entire range of possible graph structure constellations including directed, undirected, mixed graphs, hypergraphs, and application-specific attributes.

Overview
A GraphML file consists of an XML file containing a  element, within which is an unordered sequence of   and   elements. Each  element should have a distinct   attribute, and each   element has   and   attributes that identify the endpoints of an edge by having the same value as the   attributes of those endpoints. Here is what a simple undirected graph with two nodes and one edge between them looks like:

Additional features of the GraphML language allow its users to specify whether edges are directed or undirected, and to associate additional data with vertices or edges.