Errata

Corrections to the first published edition of Datalevin: The Definitive Guide. Corrections listed here are also applied to the source for the website and future editions.

Chapter 9, §6.1: VIP silver rule

Reported: 2026-07-13
Status: Corrected in source

The published silver rule accepted a user who was either a high spender or a frequent shopper. Because a gold user satisfies both predicates, that rule also classified the user as silver.

The corrected silver rule excludes the conjunction that qualifies a user for gold:

[(vip-status ?u ?tier)
 (or (is-high-spender? ?u)
     (is-frequent-shopper? ?u))
 (not-join [?u]
   (is-high-spender? ?u)
   (is-frequent-shopper? ?u))
 [(ground :silver) ?tier]]

With the example data, the corrected result is:

#{["u1" :gold]
  ["u2" :silver]
  ["u3" :silver]}