Design of Everyday Things [68]
5.2 Wide and Shallow Decision Tree. A lot of alternatives, but after the first decision, few or no further decisions. In this menu from an ice cream parlor, there are many choices, but once the flavor has been chosen, the remaining decisions are simple—what kind of cone, how many scoops, and what kind of topping. (Photograph by the author of a sign at a Baskin-Robbins store.)
Another example is the sequence of steps required to start a car. You must go to the car, select the proper key, insert it in the door lock, turn the key, open the door, remove the key, get into the car, close the door, put on the seatbelt, insert the proper key into the ignition, make sure the car is not in gear, start the engine, and so on. This is a deep structure, but it is narrow. There is a long series of steps, but at each point, there are few, if any, alternatives to consider. Any task that involves a sequence of activities where the action to be done at any point is determined by its place in the sequence is an example of a narrow structure.
jnd Cabrillo Sea Bass jnd Jalepeño Sauce
Saute onion and garlic. Chop 1 large onion.
Heat 2 bottles of beer to boiling. Peel and chop 6 tomatillos.
Place sea bass in pan. Slice 2 Jalapeño chiles lengthwise.
Pour beer over fish. Peel and quarter 2 tomatoes.
Add onion, garlic, and mushrooms. Place onion, tomatillos, chile, and tomatoes in sauce pan.
Add 4 whole garlic cloves, unpeeled.
Add cilantro. Cover with 1 cup red wine.
Poach for 10 minutes (approx.) Simmer for 15 minutes to 2 hours (the longer the milder).
Remove fish from pan.
Reduce stock over high heat. Add cilantro.
Put brown rice on serving plate. Serve.
Place fish over rice.
Cover fish with stock and jndJalepeño sauce.
5.3 Deep and Narrow Decision Tree. Few decisions need be made at any level, but to complete the task, many steps (levels) must be followed. This decision structure is characteristic of any task that has a large number of steps, each of which is relatively straightforward. An example is the steps required to follow a recipe, such as my favorite fish recipe.
The modern superhighway offers the driver a series of exits. The driver either starts on the road with a predetermined exit in mind or else must decide at each exit whether to stay on the road or not. In fact, road designers attempt to linearize and simplify the decision-making tasks of the driver: the relevant information is fed slowly and sequentially to the driver to minimize the mental workload and the need for overlapping processing.
Freeway design is by now a science, with a well-defined set of procedures and with societies, books, and journals devoted to it. Different countries of the world have reached different solutions to the problem of guiding the driver,
A rather complete analysis was done in Britain for the design of the M series motorways. Each motorway exit has a carefully programmed sequence of six signs. The first precedes the exit by one mile and is intended to serve an alerting function, as well as to present route number information. The second precedes the exit by a half mile and gives the major towns reached by the exit (but no route number information). The third precedes the exit by a quarter mile and adds the “forward destination” (where you eventually get to if you don’t exit). The fourth sign is at the exit and provides major route numbers and a few town names. The fifth sign is on the motorway beyond the exit; it is intended to play a “confirmatory” role: it displays the forward destinations and their distances. The sixth sign is on the exit ramp, in colors the reverse of all the preceding signs; it shows all the local destinations, usually on a map of the roundabout (traffic circle) found at most exits. 10
THE NATURE OF EVERYDAY TASKS
Most tasks of daily life are routine,