SAS isn't really a database product, although it works on/with databases.
TDWI is the Data Warehousing Institute. They are the data warehousing group that I personally find to be the most useful. Sometimes they get a wee-bit over excited pitching their classes and conferences, but their overall signal to noise ratio is the best that I've found.
Actually it is a lot cheaper to license SAS now than it was even a few years ago. That's a relative statement, in that it still isn't cheap, but at least now you don't have to mortgage your first born to have a shot at it.
I'm not sure what you mean by "what is the specialization field for SAS?" SAS does one thing, statistics. It can find patterns in data that looks like pure chaos, and in the hands of someone that knows how to use SAS, it can make the process seem effortless.
If you need SAS, it would be cheap at twice the price. If you don't need SAS, it is a very, very expensive decorating accessory.