Where does the Heimerdinger offense come from?

We've all seen the trees that link Bill Walsh to George Seifert to Mike Holmgren to Jon Gruden and what not, but I don't know where Heimerdinger's offense comes from?  Is it a variation of Denver's or does it have roots in something like the Paul Brown regime?  The two things we can say with certainty is that it has nothing to do with the West Coast offense and that it is working well.

If anyone can illuminate this for me, I'd appreciate it.