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DOT is a plain text graph description language. DOT graphs are typically files with the file extension gv or dot. The extension gv is preferred to avoid confusion with the extension dot used by early (pre-2007) versions of Microsoft Word.
Contents
- Undirected graphs
- Directed graphs
- Attributes
- Comments
- A simple example
- Layout programs
- Limitations
- References
Various programs can process DOT files. Some, such as OmniGraffle, dot, neato, twopi, circo, fdp, and sfdp, can read a DOT file and render it in graphical form. Others, such as gvpr, gc, acyclic, ccomps, sccmap, and tred, read DOT files and perform calculations on the represented graph. Finally, others, such as lefty, dotty, and grappa, provide an interactive interface. The GVedit tool combines a text editor with noninteractive image viewer. Most programs are part of the Graphviz package or use it internally.
Undirected graphs
At its simplest, DOT can be used to describe an undirected graph. An undirected graph shows simple relations between objects, such as friendship between people. The graph keyword is used to begin a new graph, and nodes are described within curly braces. A double-hyphen (--) is used to show relations between the nodes.
Directed graphs
Similar to undirected graphs, DOT can describe directed graphs, such as flowcharts and dependency trees. The syntax is the same as for undirected graphs, except the digraph keyword is used to begin the graph, and an arrow (->) is used to show relationships between nodes.
Attributes
Various attributes can be applied to graphs, nodes and edges in DOT files. These attributes can control aspects such as color, shape, and line styles. For nodes and edges, one or more attribute-value pairs are placed in square brackets ([]) after a statement and before the semicolon (which is optional). Graph attributes are specified as direct attribute-value pairs under the graph element. Multiple attributes are separated by a comma or using multiple sets of square brackets. Node attributes are placed after a statement containing only the name of the node, and no relations.
HTML-like labels are only available on versions of Graphviz that are newer than mid-November 2003. In particular, they are not part of release 1.10.
Comments
Dot supports C and C++ style single line and multiple line comments. In addition, it ignores lines with a number sign symbol (#) as their first character.
A simple example
Following is an example script that describes the bonding structure of an ethane molecule. This is an undirected graph and contains node attributes as explained above.
Layout programs
The DOT language defines a graph, but does not provide facilities for rendering the graph. There are several programs that can be used to render, view, and manipulate graphs in the DOT language:
Limitations
It is possible to specify layout details with DOT, although not all tools that implement the DOT language pay attention to the position attributes. Thus, depending on the tools used, users must rely on automated layout algorithms (potentially resulting in unexpected output) or tediously hand-positioned nodes.
For example:
There are two problems in the image above. The square on the right is not a perfect square and the label "(g o f)'" is in the wrong place.
This can be fixed with Inkscape or other SVG editors. In some cases, this can also be fixed by using the pos attribute to specify a position.