“Workplace violence” could be an umbrella term to describe what happens in the workplace, but when we talk about “harassment” or “bullying” or “mobbing”, people interpret them in different ways. When you try to compare data between institutions, that's where the problem lies.
Let's say that for the term “harassment” the definition should include that it's repeated behaviour. If it's a one-time deal, then it wouldn't be called harassment. Maybe if we had some little terms that would discriminate between these, we would know what is meant by all the terminology. I see violence as being on a continuum, and there's escalation; for some people, incivility is considered violent, and for others it's not. That's where things get murky.