(derive :e/article :e/publication)

(defmethod validate :e/article [x]
   ((get-method validate :e/publication) x)
   …)

(defprotocol Validatable
  :extend-via-metadata true
  (validate [val]))

(def blank-publication
  (with-meta {} {`validate (fn [x] x)}))

(def blank-article
  (vary-meta blank-publication update `validate
             (fn [old]
               (fn [x]
                 (old x)))))

(def article-validations [validate-word-count])
(def photo-validations (conj article-validations validate-total-weight validate-copyright))

(defn validate [article]
  (reduce (fn [[article validation-data] validator] (merge validation-data (validator article)))
                 [article {}]
                 photo-validations))