References:

• Each experimental protocol has been added by a user (1:N)
• Each sample follows an experimental protocol, and has been done by an user. However, the user is not necessarily the owner of the experimental_protocol (1:N)
• Each sample can have several protein sequences (1:N)
• Each protein sequence can be related to one or more identified proteins (1:N)
• Both experimental protocol and identified protein will have a reference (1:N)