Chapter 1: Users

"Beware the Jabberwock, my son!
  The jaws that bite, the claws that catch!

The saying goes: "Business would be great if it weren't for customers." Well, programming would be easy if it weren't for users. In the simple case, there would be exactly one user for your program, - yourself - and you would use it only once. Most programs, however, are used many times by many people. You must take those users into account when designing your program.

This chapter will only review those aspects of users that are most relevant to text editing: full discussions of users and design can and do fill many books in themselves, some of which are listed in the Bibliography. This chapter (and this book) does not address the question of non-people users.

User Categories

Each user can be placed in a category. Each category is described in terms of the amount and the type of experience. It is important to understand users: each user creates a model of how a new program works based on his or her experience with other programs combined with the "hints" that your program's user interface gives to him or her. It is up to you to either match your program's behavior to your users' model(s) or to give them enough information so that they generate a model that is well-matched to your program.

Amount of Experience

The amount of experience that a user has is a point on a continuous scale. All users start with no experience and accumulate experience as they learn. Although the scale is continuous, I have divided it into five regions in order to simplify discussion. Also, this list is not intended as a self-rating scale: most of you who are reading this book will be programmers.

Neophyte users barely know what a computer is. They lack understanding of such "basic" terms as "file" and "file name" (the concepts behind these terms are actually quite sophisticated). This lack of understanding does not mean that they are unintelligent people, only that they have never had a reason to learn these concepts. If you are designing a program for this type of user, you may feel both blessed and cursed. Cursed because it can be so difficult, and blessed because this area of program design has such a pressing need for good designs.

Experience from the field of artificial intelligence can shed more light on this issue. AI researchers found it (comparatively) easy to write programs that can handle advanced mathematics such as freshman calculus. However, as the researchers pushed on to handle such easy (to most people) areas as filling in coloring books, the programming problems got harder and harder. Some of this difficulty is due to the fact that the task of teaching college-level courses is well understood--especially by college professors--but teaching coloring is not. For example, how many textbooks have you seen on "how to color"? More to the point, computers have been designed to process information in a certain way, one that is mathematically elegant, but not necessarily related to how people's minds work. As people write programs for more and more "basic" tasks, this difference becomes increasingly apparent.

Many programs have been (mis-)designed for neophyte users. They often offer a few simple commands, yet leave intact such difficult concepts such as that of a "file." They solve the wrong problem, sort of like travelling to a place where a foreign language is spoken, and trying to communicate by speaking your native language slowly and distinctly. As a program designer, you must understand the thought structure of your users, and design programs that match that structure. The blessing comes from designing programs that are very different from "conventional" programs and which are well-matched to their users.

Novice users have used a computer before, perhaps for text editing, word processing, spread sheet, or database applications. In any event, novice users have some familiarity with the idea of typing things into a box and seeing a response that somehow reflects their typing. They understand how a shift key works, that a lowercase letter 'l' is not the same as a digit '1', and so forth. They even have some understanding of the idea of "context:" that keys do different things at different times. Users with this amount of experience are able to operate almost any program that has a good design and a decent manual.

Basic users are like novice users, only more so. They understand such programming concepts as thread of control, variables, and statements like "A = A + 1" (in fact, many people call such users "programmers"). These users can operate any program, even one with a poor design. Given source code to the program they are able to customize and extend it, albeit in what might be an awkward fashion.

Power users know one or more application programs thoroughly. They understand not only how to use those programs fully, but can often go beyond the bounds of what the original designers intended. They may write large programs often in the form of application macros, but do not design these programs. These users understand the fine points of the programs that they use.

Programmer-level users understand the theory of programming. When writing a large program, they design the program before implementing it. They generalize, applying their experience and their knowledge of one program to guess how another program will operate.

Type of Experience

The amount-of-experience scale is one-dimensional: people start at the beginning and proceed along the scale as they gain experience. This type of experience scale is more like a collection of baseball cards. A user can collect the experience types (cards) in any order, and two people with the same number of experience types (cards) may have no experience types (cards) in common.

The experience types do not necessarily carry over: experience gained on one type of system may or may not prove useful on another. Actually, experience gained on one system may make it more difficult to learn another. And, if users grow to like one type of system, they may then dislike another one, thus making any experience transfer problematic.

These experience types can have a major effect on the design of your programs, as it is usually important for new programs to appear and operate in a manner similar to existing programs. Thus, the (possibly bad) designs of those existing programs may have to be carried into the design of your program.


This section might also be titled "religious preference." In the computer field, "religion" is a technical term that refers to the usually irrational and extreme preference of one program, style, or method to another. Although you cannot really do anything about this phenomenon, you can keep it in mind when analyzing comments on your design.

It has been observed that people often "get religion" over the first application (for example, a word processor) that they use. I can't recall the number of people who have tried to convince me that the program that they just discovered (i.e., the first one they used) is the best one in the world. This form of "religion" is normal and derives from the facts that (1) the move from manual to automated methods (e.g., from typewriters to word processors) involves a major increase in capabilities: even the simplest word processor provides vastly more capabilities than does a typewriter, and (2) new users do not have the experience to realize that all programs (e.g., word processors) are not equal. This form of religion usually fades away over time as new users gain experience.

In a hauntingly close parallel to the "second system effect" (Brooks 1982), the "second program users" are the ones to watch out for. These people started using one program, then gave that program up in favor of a second one. The problem is that they think that since the second program is better than the first one (which it usually is), it must therefore be better than all the rest.

There is nothing in particular that you can do about users that feel religious about a program: rational arguments are in general ignored. You can, however, be aware that such users exist, and recognize when you are dealing with one.

User Goals

Knowing your user's experience is essential, but a program design must incorporate knowledge of what task or tasks the user is trying to accomplish. For text editors, he or she might want to create:

The frequency of doing these tasks can range from occasionally to continuously. Different tasks can be performed by the same user with different frequencies.

The style of doing these tasks can also vary. One person may do all of one task, then start on the next. Another person may be frequently switching among two or more tasks.

Physiological Constraints

Users are people. There are limits to what people can do. These limits must be considered when designing a program.

Hands have a limited reach. The very act of reaching for one key draws a hand away from other keys. Thus, commands that you expect to follow one another should be assigned with that constraint in mind. Function keys are often difficult to find and awkward to press. While there are almost always two shift keys, most keyboards only have one control (or equivalent) key and may only have one of other types of shift keys. Thus, it is difficult to press some shifted keys (such as control-P) with just one hand.

Non-keyboard devices such as mice draw a hand far away from the keyboard -- and you don't in general know whether it is the left or right hand that is drawn away. A sequence such as control-mouse button may be very difficult for some (i.e., left-handed) users to type.

Eyes can focus on a limited area of high resolution surrounded by a large area of lower resolution. However, areas of strong contrast such as reverse video are still visible in low-resolution areas. Blinking items are not only visible, but will draw the eye to them. "Status" displays should therefore change as quietly as possible so as not to draw the eye away from the text under edit. For example, it may make sense to place such status areas on the top part of the display if insert/delete line operations cause visible motion of the bottom part.

The mind (or brain), however, places the greatest constraints on editor design. It is only capable of processing a few thoughts ("instructions") per second. In order for users to be productive, it is important that these thoughts be directed as much as possible to useful editing operations. There are several things to consider regarding these thoughts.

First, mental effort (thought) is required to translate between the display representation of the text being edited and the user's internal representation. The WYSIWYG ("what you see is what you get") principle reduces this effort by reducing the amount of thought required. Note that in general WYSIWYG does not mean "fancy output on a graphics display." Rather, it means "it is what it appears to be, no more and no less."

Second, the mind has expectations: it sees (and in general senses) what it expects to see. In extreme cases, if something totally unexpected happens, it can take many seconds for the mind to even recognize that there is an unexpected image, in addition to the time required to process the image and make a decision. Thus, it is important for the program to anticipate what the mind will expect to see and to arrange the display accordingly.

Third, it takes mental effort to handle special cases. For example, if the delete operation deletes everything except for newlines, it takes effort to remember that difference and to monitor each command that is being given to ensure that it conforms to the restriction. Fourth, it takes mental effort to plan ahead. The design of the editor should make it easy for the user to change his or her mind.

Last, it takes mental effort to track modes. (Chapter 9 goes into modes in detail.) Each time a new mode is introduced, it takes mental effort to track the state of the mode and adds effort to the process of switching modes.

The mind's short-memory can hold from five to seven "chunks" of information (Norman 1990). These chunks are organized in a cache-like form. When the chunk cache fills up, chunks must be stored in "main memory," a process that takes time. Considering that some of these chunks are used to remember what is being edited, why the editing is being done, and other such context, it becomes clear that the editor should be designed to use as few of these "chunks" as possible.

The mind is poor at thinking numerically. It is much easier to think in terms of "put that there" than "put object 12856 at location 83456." These last two points mean that the computer should do as much remembering as possible for the user.

Applying These Physiological Constraints

Let us examine how these principles apply to a particular user: me. I select myself as the example for the simple reason that I understand how my mind works better than I understand anyone else's.

First, I almost always work with plain ASCII files. Hence, I can take advantage of WYSIWYG on even a simple ASCII terminal.

Second, the program/computer combination that I use can (mostly) keep up with my typing in real time.

Third, the Emacs command set that I use is very regular, so my mind need only keep track of a few special cases.

Fourth, the basic paradigm behind the Emacs command set is "move to desired position, make desired change." This paradigm applies even in the case where I made a mistake, as I simply add the mistake to the list of changes to be made and continue to apply the pardigm. I never have to change mental gears. The penalty for making a mistake is thus minimized.

Fifth, the program minimizes what I need to remember: the text being edited is there to be seen, exactly as is, and there are very few state variables to track. In addition, the Emacs command set is defined mainly in terms of objects (character, word, sentence, etc.) and has a convenient way of saying "some," "a lot," "a whole lot," and "a huge amount." (Various aspects fo Emacs command set are discussed in later chapters.)

Going beyond these principles, I have used the Emacs command set so long (thirteen years) that I quip that most of my editing is performed by my spinal cord and not my brain. Although this quip is not true since the spinal cord can only handle purely reflex actions, we will look closely at how my mind functions when editing text. The mind of any other experienced user should operate in a similar fashion.

As I write this text, part of my mind is articulating the point that I am trying to make, while another part is expanding those words into their component characters. Call these parts the "source process." Another part of my mind is translating those characters into finger motions. Call this part the "keystroke process." Other parts of my mind are reading the text as it appears on the screen, turning it back into words, and matching these words against the original word stream. Call this the "feedback process."

These three processes work in any sort of writing: using a computer, typewriter, or pen. All people who write use them. However, if the resulting text is to have few errors, one of two things must have happened: either the user made very few mistakes (thus minimizing the number of errors to be corrected) or the user must have written slowly, giving the feedback loop enough time to recognize an error before too much time has elapsed and the error becomes difficult to correct (such as an omitted character on the previous line or page).

With the advent of computers, and their ability to make seamless corrections, a third option appeared: a new, fast feedback loop. This loop operates by giving the keystroke process the ability to recognize that it made a mistake. This extra ability is not useful without seamless editing, as it takes a long time to use the eraser or correction tape. However, with (a lot of) practice, a fourth process can be "running:" the "editing process."

The editing process takes the feedback from the keystroke process and inserts editing commands into the character stream created by the source process. Here is an example of how this editing might operate to correct an error when writing the text "the quick red fox."

(Other users may have variations on this process. For example, they may always delete all of any word with an error and retype the word.) With the extra fast feedback loop, the fingers were kept typing at full speed all the time. Granted, an extra five characters were typed, but consider what would happen without the extra loop. It could well be that the entire phrase would have been typed before the error was noticed. The source process would have already started on the next phrase. When the feedback process notices the error, the smooth typing of characters would stop as the user's mind determines exactly which corrections are required and how to perform them. It must then start the pipeline going again. The stopping, correcting, and starting again takes several seconds. A fifty word-per-minute typist is typing about five characters per second. The Emacs correction string would take one second to type. There is thus a direct saving of some seconds and an indirect saving due to not having interrupted the smooth flow of thinking.

Note that the design of the command set played an important part in making this loop usable. For example, if no "go backward word" operation were available, the editing process would have to compute how many characters were in the "output buffer," an operation that is quite time-consuming (quick: how many letters in "brown"?) as well as not well matched to how the mind works.

Some recent industry trends illustrate how some "user friendly" designs clash with this editing process. Consider a typical, modern window system. In some ways, it acts to frustrate an experienced user. For example, when a user closes a modified file, the computer may put up a dialog box that says "Discard changes? Yes, No, Cancel" (or words to the same effect). This prompt will be displayed in a beautiful dialog box, neatly centered on the screen. Each response will have its own button. Unfortunately, even if the user is expecting the dialog box, he or she may have wait for the system to catch up for these reasons:

For these reasons, an experienced user's editing process may be interrupted. These interrupts no doubt contribute to the feeling of sluggishness that many experienced users still feel when using such systems. The challenge is to design your program so that experienced users can productively use your program. The steps that you can take to faciliate this use include:

In general, the goal is for an experienced user to be able to accurately predict which responses will be required, and to reliably supply those reponses in advance of the prompts. In this way, experienced users can continue to do their work, without being slowed down by the system.

Users Who Have Handicaps

When someone has a significantly reduced ability to do something, that person is considered to be handicapped in that area. The reduced ability might be physical, such as reduced hand motion or poor eyesight, or it might be mental, such as a reduced ability to remember things.

While the number of people who have severe handicaps in many areas is small, a large number of users have at least limited handicaps in a few areas. As it is important for programs to accommodate as wide a range of users as possible, programs must accommodate users with handicaps.

It is also important to keep in mind that those users that have severe and/or multiple handicaps can benefit greatly from the use of computers.

Sometimes, even users without a handicap benefit from designs intended to aid users with handicaps. For example, adding a wheelchair ramp to an old building also allows other people to roll heavy objects up the ramp instead of having to use stairs.

The main design principles to follow to take into account users with handicaps are:

It is not surprising that these are also good design rules for users without handicaps.

Questions to Probe Your Understanding

(Some of these questions refer to marketing decisions. A designer must also take into account those people who are not yet users. Remember that purchasers are "users" too.)

Consider the case where the higher you go in an organization, the less computer experience people have. Assume that product purchase decisions are made at a higher level than the product user. How does this inversion affect product design? Product marketing? (Medium)

Many product reviews include "feature checklists" or "scoreboards." These checklists in general include all features found in all related products. What are the pros and cons of these checklists for manufacturers? For users? (Medium)

I have observed that, all other things being equal, people will buy the more expensive of two application programs. Why? (Easy)

Productivity falls off as computer response time increases. However, the fall-off is not linear, but happens in a series of thresholds, where slight increases in response time cause large drops in productivity. Why do these thresholds exist? What information do you need about human physiology in order to calculate where the thresholds are? (Hard)

How would you design a program to best be used by someone with dyslexia? What about the entire computer system? It is okay to be extreme and to make it less usable by other people. (Medium)

Copyright 1999 by Craig A. Finseth.

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