With NULLs allowed:	 
user (id*, firstName, middleName. lastName)
      1    Jim        F.          Martisnon
	  2    Cher       NULL        NULL
	 
Without NULLs allowed:	 
user (id*, firstName)
      1    Jim 
	  2    Cher

usermiddle (id*@, middleName)
            1     F.

userlast (id*@, lastName)
          1     Martisnon


https://docs.microsoft.com/ example
UNF:
Projects(ProjectId, ProjectName, CustomerId, CustomerName, Activities(Activity1Id, Activity1Name, …, ActivityNId, ActivityNName), Employees(Employee1Id, Employee1Name, …,  EmployeeNId, EmployeeNName), WorkDate, TimeSpent)
1NF
Projects(ProjectId*, ItemId, ProjectName, CustomerId, CustomerName, ActivityId*, ActivityName, EmployeeId*, EmployeeName, WorkDate, TimeSpent)
2NF
Projects(ProjectId*, ProjectName, CustomerId, CustomerName) 
ProjectDetails(ProjectId*@, ItemId, ActivityId*, ActivityName, EmployeeId, EmployeeName, WorkDate, TimeSpent)
3NF
Projects(ProjectId*, ProjectName, CustomerId@)
ProjectDetails(ProjectId*, ItemId, ActivityId*@, EmployeeId@, WorkDate, TimeSpent) 
Customers(CustomerId*, CustomerName) 
Activities(ActivityId*, ActivityName)
Employees(EmployeeId*, EmployeeName)