I don't have any source I am able to share at this time, but I can share the core idea with a simple example.

Assume you have a business app where you need to conditionally do a thing. The predicates (conditions) for this thing can be expressed in terms of constraints in a SQL query, the result of which is a scalar value representing true or false. All complex decision trees can ultimately be turned into combinations of these things.

An example of this could be a decision point in a business app where you need to determine if the user should be allowed to proceed into a certain feature. Perhaps you call this knowledge IsUserAllowedIntoFeatureA. What we would do is expose a configurable SQL rule which allows for a business analyst to customize the behavior of this fact per-customer:

  SELECT 1 --1 == true, 0/null/empty == false
  FROM --My Domain
  WHERE --My Conditions   

The above SQL query would be run against a SQLite database that is mapped out of the current instance of that user's state. Once we determine the outcome, we throw away the database.

This idea can also be extended to strings, arrays, etc.