This is a rich topic and great question, one to which we should all try offer answers.
From my experience, I work with topic maps - extremely rich knowledge graphs, and an ISO 13250 standard, and I work with NLP, which entails a lot more detail than just talking about relations: they are first class citizens (subjects) in a graph, not just labeled arcs. I spoke about them here [1]
[1] https://www.slideshare.net/jackpark/lbd-tm2