A FlyerTalk Posting Legend
Join Date: Sep 2002
Location: LAX/TPE
Programs: United 1K, JAL Sapphire, SPG Lifetime Platinum, National Executive Elite, Hertz PC, Avis PC
Posts: 42,200
There is no shared database, except the No Fly List.
Each airline has a collection of similar flags, blessed by the TSA, which they use to identify customers for secondary.
They include things like...
* Last minute purchase (includes rebookings, re-routes)
* One-way tickets
* Cash paid tickets
* Frequent seat changes
Each airline applies the criteria to customers as they see fit.