To kind of illustrate what I mean, say that you have a group of students and a group of professors in some kind of a traineeship. Every professor is to mentor one student and every student has to be mentored by one and only one professor. Thus, we have an obligatory one-to-one relationship. Let’s furthermore say that you every student has a studentID (primary key), name and a phone number, and every professor has a professorID, name and a phone number. In this scenario, would it make sense to have a single table where you list all the attributes for a single entity (that is, studentID, their name, phone number, the ID of their mentor and then their name and phone number)? My first thought is that this kind of scheme breaks the 3rd normalization form, as the professor’s name and phone number are dependent on the professorID, and that perhaps splitting the table into two, having a Professor table that contains the professor’s name and phone number and putting the professorID into the student table as a foreign key is the proper way of going about it. At the same time, since it’s an obligatory one-to-one relationship, would that even matter?