Abstract: A facility for assessing availability of an item for purchase from a merchant using a model of the availability of the item is described. The facility receives asynchronous messages identifying changes in the merchant's inventory for the item that affects the availability of the item for purchase from the merchant. For each received asynchronous message, the facility updates the model to reflect the changes in the merchant's inventory identified in the message. The facility then evaluates the state of the model in order to assess availability of the item for purchase from the merchant.

Abstract: A facility for processing a request for information about a specified item is described. The facility receives the request from an originator. In response to receiving the request, the facility generates a response to the request that contains information about the specified item. The facility also determines a current level of availability of the specified item, and, based upon this determined level of availability, determines, for each of a number of ordering actions, whether the ordering action is currently available for the specified item. For each ordering action determined to be currently available for the specified item, the facility augments the generated response by adding a control for performing the ordering action. The facility sends the augmented response to the originator of the request.

Abstract: A facility for assessing availability of an item for purchase from a merchant using a model of the availability of the item is described. The facility receives asynchronous messages identifying changes in the merchant's inventory for the item that affects the availability of the item for purchase from the merchant. For each received asynchronous message, the facility updates the model to reflect the changes in the merchant's inventory identified in the message. The facility then evaluates the state of the model in order to assess availability of the item for purchase from the merchant.