Thanks to the Guitar Pro software and it's great scale, chord and arpeggio list, I finally understood this!
However, there is this one thing that bother me; how come 7ths are not included in the list?
I got the latest version of Guitar Pro (6) and I'd be shocked if something like that is lacking from software!
Something that could be it is 7 tetrachord, which is dominant, and the stuff below the notes (if the root note is C) says P1,M3,P5,M7, which somehow looks samiliar to what I mentioned in the previous post.
I'm pretty sure on this, but it would be great if someone more experienced could confirm it!