A file with a .dat extension is a data file.

When you look inside (in Notepad perhaps) you just see sort of a flat file representation of database records to be with columns separated by spaces and rows by line returns and no indication as to where the data is meant to go live beyond perhaps the name of the file itself. How the data gets used is not dependent on any one program. The .dat convention really is just a convention for passing data around and how it gets sucked into something else is up to you.