PKMS with labelled edges/links in graph view?

I'm looking for a PKMS where you can label your edges/links in graph view. For example, let's say Note 1 was about a person and Note 2 was about an event. You could link the two and label the link "attended". In graph view, you'd see the below, where the link line was labelled with the nature of the link.

|Note 1, about a person| --------- ATTENDED------|Note 2, about an event|

I know you can do this with a graph database, but those apps impose a lot of structure on your data.