Graph drawing and editing tools typically have their own graph specification format. The format has typically a textual representation that is easy to read and write. The benefits of this approach are twofold. Humans can write their own graph specification directly in the graph format (without necessarily using a graph editing tool) and tools can easily generate and parse graph data. On the downside, these formats are not space efficient. Graph formats share the following characteristics: (1) Expression of arbitrary graphs, (2) distinction between nodes and edges, and (3) attribution of nodes and edges.

(Quoted from ExchangeFormatBibliography)

-- HolgerKienle