Tool for generation of function or data flow diagrams

Question

I am looking for a command line tool which can generate function flow diagrams from some textual description (any sort of markup language would do).

The idea is to document the data connections between some components. The resulting diagrams shall resemble the following. This is mostly for own internal doc. so it doesn't really need to generate fancy diagrams. Blocks with annotation, connections with annotation and maybe some notes is definitely sufficient.

http://www.automation.com/images/article/mathworks/MathWorks_Simulink_robot_arm_simulation_model.png

http://www.randservice.com/images/screen2.jpg

Thanks a lot in advance,

Paul