The number of source instances that can be linked to each target instance. 0.1 = the link is optional; 1 = there must always ...

The number of source instances that can be linked to each target instance. 0..1 = the link is optional; 1 = there must always be one source for each target; n..m = there must be at least n and at most m. The upper value m can be *, meaning no limit.