Connecting Widgets

My project is about drawing ER Diagrams, for this I am using GWT. For now i have most of the frontend working. Now I want to have lines connecting two widgets to create a relationship between the entities and attributes. For that I want to create 4 corner points to which the lines c开发者_高级运维an connect (Technology something similar to EDrawMax or DIA).

example picture example picture http://www.cs.uofs.edu/~sudhakaras2/Example.jpg

Thank you.

If the corner stuff is optional, gwt-diagrams might be a good and clean option. Check the demo here.