S&P to start commercial real estate price indexes

I like this idea. S&P is going to start 10 new indexes today to try to track commercial real estate prices by region and by sector. Where they are going to get the information remains a little unclear. Will it come from the public records, from brokers, from parties to the deals (notwithstanding the typical confidentiality clauses), from lenders or from a some or all of the above? I guess time will tell how accurate these indexes will be, but anything is a start. I'd also be interested in learning the methodology of calculating prices back to 1993, and whether there will be a factoring for deal size or for corporate transactions such as portfolio purchases where the value of each asset is not always allocated (though it usually has to be for real estate transfer tax purposes).