<p>A ticket change constrainer which allows reissuing or revalidating an already issued airline ticket is described. It includes a ticket change domain reducer operable to reduce an input search domain of change opportunities on the basis of change conditions set in the already issued ticket. It also includes a ticket change valuer operable to weigh the change opportunities of the reduced search domain and to return a reduced valued search domain of change opportunities. The weighing of the change opportunities is done on the basis of pricing method popularity scores updated in a ticket change memory by a ticket change watcher agent from actual change transactions handled by the system. The change conditions include standard pricing methods of the airline industry. The input search domain of change opportunities is produced by a conventional fare-driven search engine on the basis of a ticket change request issued by an end-user of the system. The reduced valued search domain of change opportunities returned by the ticket change constrainer always includes a lowest fare opportunity compatible with the change conditions set in the already issued ticket.</p>
