Its great that Yed supports the Barker ERD "crows foot" diagramming style (http://en.wikipedia.org/wiki/Barker's_Notation).
However one element of this notation doesn't appear to be supported by yEd - the exclusion arc. See the heading "exclusion arcs" on this page for a description: http://www.entitymodelling.org/part-two
I can find no way to draw such a line in yEd. Thoughts on how I can do this?
There is no support for this kind of element in yEd, I'm afraid. At least not at the moment.
Short of a better idea, you could try to model it using an arc edge between two invisible nodes, however, that obviously would only be a workaround...