@Ramin
Actually I have never seen such a library.

What I have done in the past (3 years ago) was to draw some elements connected to each other using Qt Quick (QML) and it worked pretty good.

Another option is to look at the new modelling plugin that will be part of Qt Creator 3.6. And since Qt Creator is open source, you can look at how it is done and perhaps use that as a starting point.