Let's look at a few specific models that have been very successful in multiple applications. They range from easy and very inexpensive to build, to sophisticated work requiring substantial investment. All of them, however, have been very successful (as in getting people to do the right thing at the right time) and have been used with a wide variety of content. Once built, their repeated use has made them very affordable.
Sometimes complex tasks have to be overlearned so as to become almost automatic—such that they can be performed accurately with little thought even under stressful or distracting circumstances. Airline ticket agents, for example, often have to work their computers to locate and enter information while people are talking to them, reciting numbers and information not yet part of the transaction or making friendly but nevertheless distracting conversation.
Reservation and ticketing operations can be complex, requiring multiple steps, interpreting codes, responding to restrictions, looking for options, and so forth. Interfaces vary from more prompted and helpful designs to those that originated years ago, when a coded, invariant syntax was used. An acceptable entry, such as the one below for simply retrieving a reservation record, had to be keyed exactly as shown or it was completely rejected:
* indicates a display operation, 122 is the flight number, 17SEP is the date (September 17), ...