How Does Comping Software (Privy, Propwire, Propstream) Get Their Data?

[Tim Tafel]

I'm trying to understand how they collect data so as to develop the best comping practices. It seems to me that they all whether paid of free, will all have the same exact amount of houses because all the transactions are all public and so they seem to compete with each other based on the quality of the data of the houses, how up to date it is, and the user experience in configuring the how the layout is. Is that correct or am I way off?