Attribute `protocol` is part of the `Sample`, but unused

Could you please motivate the protocol attribute on the Sample class?

I'm a bit confused on reasons of having a sample know which protocol they belong to. In theory, a database sample can participate in multiple dataset splits, so it is confusing to have this association at this level.

As a further note, you have:

Class X:
  
  def __init__(self, a, b, c):
    self.a = a
    self.b = b
    self.c = c


Class Y:

   def __init__(self, a, b, c):
     self.a = a
     self.b = b
     self.c = c

x = X(1, 2, 3)
y = Y(x.a, x.b, x.c)

Where as, if you'd like to associate things from X back to Y, you should just do that:

Class X:
  
  def __init__(self, a, b, c):
    self.a = a
    self.b = b
    self.c = c


Class Y:

   def __init__(self, x):
     self.x = x

   @property
   def a():
     return self.x.a

x = X(1, 2, 3)
y = Y(x)

IOW, the Sample class needs to know about the datadir and protocol so, it is better to associate the Sample to the Database object directly instead of the individual bits all the time.