As a simpler (in the Hickey-sense) alternative, he lists rule systems and logic programming. For example, keeping parts of the business logic ("What do we consider an 'active' user?", "When do we notify a user?", etc...) as datalog expressions, maybe even storing them in a database, specifies them all in a single place. This helps to ensure consistency throughout the program. One could even give access to these specifications to a client, who can then customise the application directly in logic, instead of chasing throughout the whole code base.

Basically everyone involved agrees on a common language of predicates explicitly, instead of informally in database queries, UI, application code, etc...

But Hickey also notes that this thinking is pretty "cutting-edge" and probably not yet terribly practical.

core.logic https://github.com/clojure/core.logic core.match https://github.com/clojure/core.match

1: https://clojure.github.io/core.logic/