> Include an Hardware Asset FK in your Link M2M table. Model each binary link explicitly, so a Y cable = 2-3 different Links that point to the same cable Asset. Or you can have single Links with M2M inputs/outputs. But definitely don't model Y cables explicitly.

Our cables have stickers with cable IDs, which are stored in the CMDB (and can be used to trace the endpoints through patch fields, for example).

So if you model a Y cable as two physical cables, you have to both allow duplicate cable IDs AND multiple cables per port. Both of these have significant downsides in preventing data entry errors.