Re:Three-Valued Logic
by chx on Friday December 15, 2017 @09:09AM
(#15931859)
Drupal 8 access check system uses 3VL as well: Allowed, Forbidden, Neutral. What I found interesting is the only difference between AND / OR is the Allowed - Neutral case: OR resolves that as Allowed while AND resolves that as Neutral. Otherwise, X AND/OR X is obviously X and F AND/OR X is F. Sounds quite logical but the truth table does look weird with so little difference.
In other words, at the end of the day, when making a decision to deny or grant access using a bunch of these 3VL checkers, you use two rules: 1. If anyone forbid, then it's a deny. 2. If no one forbid, if running OR then you need at least one Allowed when running AND then you need to have all of them saying Allowed.
In other words, at the end of the day, when making a decision to deny or grant access using a bunch of these 3VL checkers, you use two rules: 1. If anyone forbid, then it's a deny. 2. If no one forbid, if running OR then you need at least one Allowed when running AND then you need to have all of them saying Allowed.