I would say all of them can be model as functions.
model number:
This would be a onto function, meaning that the outputs are not unique.
f(model_1) = f(model_2) = computer_type.
part number:
This would mean the function takes in multiple parameters.
f(part_1, part_2, part_3, ...) = computer
serial number:
This is the most obvious one; an one-to-one function:
f(s_num_1) = computer_1;
f(s_num_2) = computer_2;
