Link of uploaded documents

Could you please inform me or refer me to a doc. 

I need to know where and how an uploaded document is linked to the entry  

Example   if in a payment entry, the suppliers invoice is uploaded as a document, where in backend does it refer to that entry?

Document name? Location of uploaded document? Database entry ? 

Tx

The Laravel Mediable is used there https://github.com/plank/laravel-mediable