Create relationship diagrams with Graphviz
If you use charts to represent relationships between data or objects in presentations or project reports, try Graphviz. Licensed under the Common Public License Version 1.0, Graphviz is visualization software, designed to help you easily create structural information. You can use it to visually represent database and table relations in a project report or a simple Web site hierarchy.
Installing Graphviz is a breeze, especially if you are running a Debian-based distribution. Just run apt-get install graphviz. You can also download RPM or source files to set it up.
Graphviz comprises a collection of tools you can use to create graphics with lines or arrows between objects. Graphviz calls these undirected and directed graphics, respectively. One of these tools is dot, which accepts input in the C-like dot language. Dot is highly customizable, allowing you to control line colors, arrow heads, node shapes, and other items in your graphic.