Design Trade-offs

The decision to limit TURBOMail to strictly domestic parcels arises from a lack of knowledge about the way international mail is handled. Certainly, contents declarations must be filled out which cannot be handled by a machine (it is preferable to have a human operator inspect packages to see if suspicious signs are present), but the primary reason for this restriction was to maintain simplicity of the interface. Since postal rates may vary with the country of destination, such information would have to be entered into the system. Such information could not be accomplished by a simple button interface. It would require the use of a keyboard (name entry) or a pointer (geographical entry by selection on a map), and neither interface is particularly elegant for the given task. Keyboard entry of geographical names runs the risk of common typing errors or spelling differences/variants, while selection on a map may simply not be in the knowledge of the user (people send mail to cities whose names they know, but they may not know the actual location of the city on a map).

Money orders also are not handled by the TURBOMail system because of a lack of knowledge of how they are handled. If the recipient of the money order must be clearly stated at the time it is filled out, a keyboard is required for this information, and keyboards have been excluded from the design to simplify the interface.

The use of a hybrid menu-based and question/answer interface limits the control flow of the system and prevents experienced users of the system from proceeding directly to the point of the interface that they want. However, given the simplicity of the system and the relatively small number of steps to perform any given task, we feel there is little inefficiency introduced by such limitations.

There is no current provision for a user who has already placed postage on a parcel to evaluate it using TURBOMail and then buy an incremental amount of postage to cover a difference between the postage present and the required postage; such a customer must return to the system main menu and then purchase the requisite amount of postage. We feel that imposing an additional memory task upon the user is a smaller burden than additional interface complexity (purchase full amount/purchase incremental amount) which may be caused by allowing a second option which may be conceptually ambiguous to the user at first glance ("Why would I not want to purchase the full amount of postage? Is this some sort of discount?").

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