Dialogue design

Dialogue design

49.1 Purpose

A dialogue is the exchange of information between a computer and a user. This chapter discusses several different types of dialogues and the dialogue design process.

49.2 Strengths, weaknesses, and limitations

This chapter introduces some important principles of dialogue design. The strengths, weaknesses, and limitations associated with specific dialogue types and dialogue design techniques are discussed in context.

49.3 Inputs and related ideas

Dialogue design is typically performed in the context of user interface design (Chapter 48). Dialogue design focuses on the contents of specific screens, while interface design is more concerned with defining the structure, the links, and the execution sequence associated with the complete set of screens and windows that defines a user interface. To put it another way, dialogue design is concerned with the data, while user interface design is more action-oriented.

Much of the specific information needed to define the dialogue is collected during the problem definition (Part II) and analysis (Part IV) stages of the system development life cycle. Dialogues often utilize windows (Chapter 50). Data entry concepts are discussed in Chapter 46.

49.4 Concepts

A dialogue (or dialog) is the exchange of information between a computer and a user. Reports, forms, and individual screens are static; think of them as individual slides or still pictures. A dialogue, in contrast, is dynamic and interactive.

Dialogue design is closely linked to user interface design (Chapter 48). During the user interface design process, the designer identifies the necessary screens and defines how those screens are linked. During the dialogue design process, the designer creates the contents of those screens.

49.4.1 Types of dialogue

The purpose of instruction dialogue (sometimes called the systems information interface) is to provide instructions and other information about the system’s operations, functions, and structure. The information might be presented in text or graphic form (e.g., a hierarchy chart or a table of menus). The taskbar that shows the open or active programs at the bottom of a Microsoft Windows 95 screen and a detailed Microsoft Word help screen on a particular topic are good examples.

Assistance dialogue is an interactive process intended to help the user find something; the help index and the little character in the corner of a Windows 95 screen are good examples. Note that the detailed explanation displayed at the end of the help process is instruction dialogue. Assistance dialogue normally requires a response of some type; instruction dialogue often does not.

Question-answer dialogue is designed to solicit user input. Action-oriented question-answer dialogue requires only a single keystroke. For example, in many situations, typing Y (for yes) or N (for no) provides the system with enough information to trigger an action, and typing a single letter or digit is often enough to select a choice from a list of options. Information-oriented question-answer dialogue asks the user to provide more information (a sentence, a paragraph, some data), and the input information is generally not used to directly trigger execution. For example, Figure 49.1 shows a portion of the Library of Congress Advanced Search screen.

Figure 49.1  A portion of the Library of CongressAdvanced Search screen showing an example of information-oriented question and answer dialogue.

Explanation dialogue is widely used in multi-media and other hyperlinked structures. The supporting material appears in a separate window or screen and provides a sentence or a paragraph of explanation, often for a hot word or hot phrase. In effect, explanation dialogue performs a glossary function. For example, when the mouse is held on a Microsoft Windows 95 icon, a brief description of the icon’s function appears in a small dialogue bubble. The status window that appears on some mailers after an e-mail message is sent is another example.

Graphics display dialogue is common in installation or system evaluation routines. For example, the bar chart near the bottom of the FORMAT window in Figure 49.2 gives the user a clear sense of the progress of a format operation. The animated bar chart that shows percent completion while an installation routine runs is another example.

Figure 49.2  A Microsoft Windows 95 FORMAT window.

49.4.2 Dialogue design issues

An ideal dialogue is consistent (in sequence, operation, and/or execution), easy to understand, and easy to use. Each element of the dialogue is built from simple, easy-to-understand, grammatically correct sentences. Computer jargon and abbreviations are used only when absolutely necessary. As a minimum the user is able to exit (or escape) and undo (undelete or cancel) any operation without losing already completed work. The elements of the various dialogues are grouped in a logically consistent manner. When errors must be communicated (for example, through assistance dialogue), all errors are identified and clearly defined, and consistent terminology is used to describe the errors.

Feedback is essential. The user should always be given status information, clear and appropriate prompts and cues, and (when necessary) clear warning messages.

Data entry (Chapter 46) should always be verified. Validity tests are used to ensure that each input field is the right type (numeric, alphabetic), that the value of a given field is within upper and lower bounds, that fixed length fields (e.g., social security number, telephone number) are the right length, and so on. Exception tests are used to screen such “exceptional” values as a zero in a field that will be used as a divisor. Reasonableness tests are used to screen invalid values (e.g., anything but F or M in a single-character sex or gender field). The objective is to screen out and (if possible) correct bad data before they enter the system.

Default or assumed values can help, too. For example, if an input field is empty (or null), a blank space might be assigned to a literal, and the value zero might be assigned to a null numeric field. Sometimes, default values are preassigned to a field or included in a list or menu from which the user can select. Finally, confirmation controls ask users to verify their inputs (often by responding to one or more yes or no questions) before advancing to the next screen or window.

Response time is a very important criterion for a dialogue-driven system. Traditionally, response time is defined as the interval between the instant a command is issued and the instant the response begins to appear on the screen, but that definition ignores the user. A more useful definition of dialogue response time includes the following elements:

  1. System response time—The traditional definition.

  2. The display rate—A hardware parameter that determines how quickly the complete screen appears.

  3. User scan/read time—A measure of how long it takes the user to read and understand the screen.

  4. User think time—Think time includes a cognitive phase during which the user evaluates the screen and a perceptive phase during which the user decides what to do.

  5. User response time—User response time includes a motor phase during which the user performs a physical action (press a key, point, and click) and a sensory phase during which the user waits for feedback.

  6. Error time—The time spent making and recovering from errors; this factor does not occur on all the screens. It is often expressed as an expected value (the time multiplied by the probability of occurrence).

Response time can be estimated or measured for each screen. Transaction response time is the sum of the response times for all the screens in the dialogue.

49.4.3 The dialogue design process

Dialogue design is typically performed in the context of user interface design (Chapter 48), program design, or subsystem design. The user interface design defines the required set of screens and windows and the order of execution for the various dialogue elements. A dialogue is designed and created for each screen or window in the user interface.

Much of the specific information needed to define the dialogue is collected during the problem definition (Part II) and analysis (Part IV) stages of the system development life cycle. Such design requirements as response time and throughput are key criteria, but the dialogue designer’s most important task is to study the users, their needs, their interests, and their capabilities. If the dialogue is not meaningful to the user, system performance will be negatively affected.

Once the required dialogue type is defined, the initial draft of the dialogue to support a given screen or window is often prepared using structured English (Chapter 60). After the draft version is desk checked, shared with the user, and approved, the necessary code is incorporated into the user interface prototype, tested, and modified as necessary. When an acceptable user interface prototype (with acceptable dialogues in place) emerges, the dialogues are converted into the finished code using a programming language, a screen generator, or some other tool.

49.5 Key terms

Action-oriented question-answer dialogue —

A form of dialogue that requires a single keystroke response to trigger an action.

Assistance dialogue —

A form of dialogue designed to provide help with command syntax, error messages, error identification, error symptoms, and so on.

Dialogue —

The exchange of information between a computer and a user.

Explanation dialogue —

A form of dialogue that performs a glossary function.

Graphics display dialogue —

A form of dialogue that shows information in graphical form.

Information-oriented question-answer dialogue —

A form of dialogue that asks the user to provide information (a sentence, a paragraph, some data) that is generally not used to directly trigger execution.

Instruction dialogue (systems information interface) —

Dialogue that provides instructions and other information about the system’s operations, functions, and structure.

Question-answer dialogue —

A form of dialogue designed to solicit user input.

Response time —

Traditionally, the interval between the instant a command is issued and the instant the response begins to appear on the screen; dialogue response time includes system response time, the display rate, user scan/read time, user think time, user response time, and error time.

Transaction response time —

The sum of the response times for all the screens in the dialogue.

User interface —

A point in the system where a human being interacts with a computer.

49.6 Software

Many CASE products support dialogue prototyping. Screen painters, menu builders, report generators, fourth-generation languages, and executable specification languages are popular tools for creating dialogues.

49.7 References

1.  Dewitz, S. D., Systems Analysis and Design and the Transition to Objects, McGraw-Hill, New York, 1996.

2.  Hoffer, J., George, J., and Valacicho, J., Modern Systems Analysis and Design,Benjamin/Cummings, Redwood City, CA, 1996.

3.  Powers, M., Cheney, P., and Crow, G., Structured Systems Development: Analysis, Design, Implementation, 2nd ed., Boyd & Fraser, Boston, MA, 1990.

4.  Whitten, J. L., Bentley, L. D., and Dittman, K. C., Systems Analysis and Design Methods, Richard D. Irwin (McGraw-Hill), New York, 1997.