Out of curiosity about the inner workings of my favorite hotel chain...

I noticed several references on Starwood.com to various rate codes such as RACK, SET, and COR. I know what RACK is, and I assume that COR is a corporate rate. What is SET? And are there any other known rate codes? I also found that the rate code for cash & points is SPGCP - is there then also a rate code for Starwood free nights using only points?

Thanks!