A melody can be written in a type of relative notation, where we don't think in notes but rather in relative intervals.
X - means choose any note
0 - means hit note again where you are
positive - means to raise current note by this many semitones
negative - means to lower current note by this many semitones
So the first few measures of the melody of happy birthday could be written as:
X 0 2 -2 5 -1 -4 0 2 -2 7 -2
Is there an official name for this type of notation?