Hi All, My apologies, I think I may have asked this question already, but I could not find it. Here it goes: I have seen the usage of the word 'relation', specifically a relation between tables but I have not seen a formal definition. From what I understand, tables X,Y are related to each other if some attributes A_X used in X need some of the attributes A_Y in Y in order to be "fully understood" , meaning some attribute A_yi in Y is needed as context to make sense of some attribute A_Xj in X. Formally this is expressed by the fact that an attribute in Y is used as a FK (Foreign Key) in X. As an example, I guess we could have: X is "Workers": Worker_Num (PK), Worker_FName, Worker_LName, Worker_DOB and then Y could be for info on workers: Work_Info: Work_ID , Work_HourlyPay, Work_Skill (Assuming each has just one skill), Work_Hrsweek (Assuming these are constant), Worker_Num (FK). Then Y's existence and meaning depend on X. So we say X,Y are related? And this is made formal by the fact that Y contains the FK Worker_Num ? Is this correct? Is there more/less to it than this? Thanks.