Regularly clean orphaned nodes
Resources do not need to be used in the graph, but need to exist in order to be used. This leads to nodes that are essentially "orphaned", leading to poor results in the search or "bad" (accidental) reuse. We should have a component that regularly clears those nodes, e.g. cleaning all orphaned entities older than 24 hours, every two hours. (Or some other policy that makes sense.)
The easiest one to clean are resources and literals. For classes and predicates, the check for usage is a bit more complicated. Also, it might make sense to have those around for long(er), because they could come from external ontologies.
Personally, I think resources and literals are sufficient for now. The solution could be extended easily later.
If numbers are reported in the statistics, we should only show that numbers of the entities that are used in the graph, not the "technical" total.