1 to 1 database design

Question

I have a database and normally users are the central object.
In database I have a tables roles and users in roles so I can give users different permissions on site.
But now I have one doubt.
I saw before one database with structure like this (User is in 1:1 relation to other tables):

User{UserId, Username, Email etc.}
Admin{UserId, some specific columns}
Child{UserId, some specific columns}
Admin{Parent, some specific columns}

and other tables are connected to user not through User table but through Admin, Child and admin.
Because now I design my database I have Users and user can be Admin, CompanyManager and Professor .
I wonder should I design table like I show above or just relied on roles?
What is advantage of the first approach?
And also in my business model User doesn't have to be CompanyManager or Professor so this is actually 1 to 0 or 1 design.
What is a good way to design database with scenario like this?

Answer 1

The advantage of having specific tables for certain types of users is to store information that is only relevant to that class of user.

In your example,

• perhaps all users would have a manager - so the manager ID would go in the users column.
• managers would have permissions to view certain information, so this would be handled via a role.
• only professors would have a Subject, or the "HasTenure" property. So this information would go in a professors table. Using this approach, you avoid the need to have a "Subject" column in the users table, when it is only applicable to a certain subset of users. As such you avoid a functional dependency in the users table, and a violation of 3rd Normal Form.

Answer 2

I prefer this approach:

In this way, you can easily group Roles into categories and assign them to users.