methods and apparatus , including computer program products , for updating information on a writable tag bound to an article . in one aspect , a method includes : receiving in a system first attribute information for a first article derived from data read automatically from a first tag bound to the article ; similarly receiving second attribute information for a second article ; receiving sensor information derived from a sensor coupled to the second article ; receiving relationship information specifying a relationship between the articles ; maintaining first and second virtual articles representing the first article and the second article and sensor information , respectively , and maintaining a context object representing the relationship ; recognizing an alert condition relating to the first article ; generating updated attribute information ; detecting the presence of the first tag at a tag writer station after the alert condition ; and causing the tag writer station to write the updated information to the first tag .