Human-Computer Interaction 3e Dix, Finlay, Abowd, Beale

exercises  -  7. design rules

EXERCISE 7.1

7.1 What was the problem with the synthesis example comparing a command language interface with a visual interface? Can you suggest a fix to make a visual interface really immediately honest?

answer

To demonstrate the principle of synthesizability within learnability, it was stated in this example that a visual interface to a file management system provided immediate information about the changed location of some file after a move operation performed by the user. In contrast, a command language interface requires the user to remember the directory to which a file is moved and explicitly issue commands to browse the directory to verify that the file has been moved. To be really sure that a move occurred, the user would also have to browse the original directory to determine that the file was no longer there. The fallacy in this argument is the assumption that visual file management systems always provide information about the new whereabouts of a moved file. To take a counterexample using the Macintosh instance from the text, if a file is moved from an open folder (in which the contents of the folder are revealed to the user) to a closed folder (contents not revealed), then the location of the moved file is not indicated to the user unless she remembers to open up the destination folder to reveal its contents. This is an example of eventual honesty and not immediate as the example suggests.

We could 'fix' this problem of eventual honesty for the visual system by demanding that the destination folder be an open folder (probably too restrictive, given the limited screen size) or by having the destination folder temporarily open up to reveal that the file is now located within it. This last suggestion is also a bit tricky, for we might still want to determine that the file no longer resides in the original folder, so we would have to be sure that the new folder did not obstruct the view of the old folder. In practice, this might be too difficult to guarantee in general.

 

EXERCISE 7.2

7.2 It has been suggested in this chapter that consistency could be considered a major category of interactive principles, on the same level as learnability, flexibility and robustness. If this had been the case, which principles discussed in this chapter would appear in support of consistency?

answer

The discussion of consistency suggested that it can take many forms, because it is usually referred to in relation to some other feature of the interaction between user and system. Mentioned already in the text we have consistency related to the following principles:

In addition, we could interpret some other principles as contributors to consistency:

Some other principles for consistency from the text and elsewhere:

 

EXERCISE 7.3

Find as much information as you can on ISO standards that relate to usability. (Hint: many standards are discussed in terms of ergonomics). How many different standards and draft standards can you find?

answer

open-ended research

 

EXERCISE 7.4

7.4 Can you think of any instances in which the 'noun-verb' guideline for operations, as suggested in the Apple human interface guidelines for the Desktop Interface, would be violated? Suggest other abstract guidelines or principles besides consistency which support your example. (Hint: Think about moving files around on the Desktop.)

answer

The noun-verb guideline suggests that we can view all operations that the user will perform as being composed of an action (the verb) acting with one argument (the noun). In the case of moving a file (or copying, for that matter), the action (move or copy) requires more than one argument. The way the move operation is performed requires the user first to select the icon for the file to be moved and then to indicate the move operation implicitly by dragging the selected icon to the destination folder. The nouns in this dialogue are the file to be moved and the destination folder. The verb is the move operation. The natural way to express this is in the order noun-verb-noun. Strictly speaking, in order to stick with the noun-verb guideline, we would have to indicate both the target file and the destination folder before indicating the move operation. That would be consistent, relative to input expression, with most other commands on the desktop. However, some principles of direct manipulation and familiarity to the user are more important. Moving files by dragging them on the desktop is very similar to the way we can pick up any object in the physical world and move it to its new location. And the dragging operation is incremental and easily recoverable; moving to one place can be undone within the same operation since the dragging can continue until the file is released.

The file-moving example is a slightly contrived one, because some could argue that there is no violation of the noun-verb guideline (hence, moving is still consistent with respect to input expression) because the verb is 'move to destination folder'. Perhaps a better example is a command to search a file system for files matching some specification. Here, the action is to do the qualified search and the argument or noun is the set of folders or volumes of the system that you want searched. Typically, this kind of operation is defined by some dialog box that allows the user to indicate in any order the specifics of the operation (the search parameters) and the folders or volumes to search. Once this unordered dialog is complete, the user then indicates that it is OK for the system to perform the operation. This kind of form-filling dialog subscribes to neither the noun-verb or verb-noun guideline; the order is more flexible for the user than consistent.

 

EXERCISE 7.5

Can you think of any instances in which the user control guideline suggested by Apple is not followed? (Hint: Think about the use of dialog boxes.)

answer

The user control guideline states that, 'The user, not the computer, initiates and controls all actions.' In the case of dialog boxes, this guideline is clearly contradicted. A dialog box can be used to indicate when an error occurs in the system. Once this error has been detected and presented to the user in the dialog box, the only action that the system allows the user is to acknowledge the error and dismiss the dialog box. The system preempts the user dialog, with good reason. The preemptive nature of the dialog box is to ensure that the user actually notices that there was an error. Presumably, the only errors that will be produced in such an intrusive manner are ones which the user must know about before proceeding, so the preemption is warranted. But sometimes dialog boxes are not used to indicate errors and they still prevent the user from performing some actions that they might otherwise wish to perform. The dialog box might be asking the user to fill in some information to specify parameters for a command. If the user does not know what to provide, then they are stuck. A lot of the time, the user can find out the information by browsing through some other part of the system, but in order to do that they must exit the dialog box (and forfeit any of the settings that they might have already entered), find out the missing information and begin again. This kind of preemption is not desirable. It is probably this kind of preemption the user control guideline is intended to prevent, but it doesn't always get applied.

 

EXERCISE 7.6

Find a book on guidelines. List the guidelines that are provided and classify them in terms of the activity in the software life cycle to which they would most likely apply.

answer

We use as a source of guidelines Mayhew's book Principles and Guidelines in Software and User Interface Design [230]. In general, all guidelines offer constraints on the design activity and so should be known during the requirements phase. In the following list, we will concentrate on what other stages (architectural design, detailed design, coding and unit testing, integration and testing) will be most affected by the guidelines. The numbers in parentheses indicate the page reference for the given guideline.

Architectural design

Detailed design

Coding and unit testing

Integration and testing

 

EXERCISE 7.7

(a) Distinguish between principles, guidelines and standards, using examples of each to illustrate.

(b) Why is context important in selecting and applying guidelines and principles for interface design? Illustrate your answer with examples.

answer available for tutors only

(a) Principles are abstract design rules which can be said to generally apply to all systems, e.g. an interface should be predictable. Guidelines are rules that are more concrete but also generally applicable, e.g. group related functional items together. Principles and guidelines are recommendations - they do not have authority. Standards are rules laid down by official bodies (such as ISO), which must be complied with; i.e. they have authority and they are more specific than the other two. Standards may outline specific orders - of display of options, for example.

(b) Both are context dependent to a degree, although principles are more universally applicable than guidelines. However, even principles are context dependent, e.g. predictability is a principle that might not apply to a computer game. Guidelines are based on psychological theory and it is important that 1. the theory is sound and that 2. the context in which the rule is applied is comparable to that of the theory. If not, the guideline may not be relevant to the particular situation. Standards encapsulate all of this.

 

EXERCISE 7.8

(a) Why are there few effective HCI standards?

(b) How do "golden rules" and heuristics help interface designers take account of cognitive psychology? Illustrate your answer with examples.

answer available for tutors only

(a) Because standards require solid and agreed upon underlying theory and, being a relatively new discipline, HCI is lacking this theory. Most HCI standards relate to more ergonomic issues (layout design, etc.) where the theory is more clearly established. However, most of the challenges to interaction involve much higher level cognitive demands of the interface, and here we do not have empirical results on cognition and interaction that would result in prescriptive standards. Our theories are improving, but we are a long way from being able to speak with the authority of standards.

(b) Golden rules and heuristics encapsulate psychological theory in design-oriented rules so that designers can apply them directly to design situations. It is necessary to be familiar with the underlying theory so that they are applied within comparable contexts but good guidelines indicate this to enable designers to select them appropriately. A simple example would be the guideline 'group related items together in menu structures', which is based upon the theory of recall being aided by the cue of categorisation. Another good example is use of visible modes so that a user will more likely be able to predict the interpretation of a given action at any time.

 

EXERCISE 7.9

Using the web design pattern language in The Design of Sites [356] produce a design for an e-commerce site for a small retail business. How well does the language support the design process?

answer

project

 

EXERCISE 7.10 [extra - not in book]

Can principles be used to prove the usability of a system? Justify your answer.

answer available for tutors only

They can't prove it but can help demonstrate it. Since principles of software ergonomics are ill defined, could argue that usability principles offer a means of defining software usability. For example:

If a system supports these principles it is more likely to be usable than if it does not.

 

EXERCISE 7.11 [extra - not in book]

The following design criterion applying the principle of learnability is part of a set of design criteria given to a student for a project to produce an electronic fashion consultant.

Learnability: ease of learning and use

Provide some constructive criticism suggesting how this design criterion could be improved.

answer available for tutors only

There are two main problems with this design criterion.

First, it is too vague. Learnability is divided into a number of other sub-properties: predictability, synthesizability, familiarity, generalizability, consistency. The criteria should be more specific. For example, is learnability important for novice users, or for experienced users who want to learn more and new features of the system? Will the learnability be achieved through consistent implementation of similar features, or will it leverage off some metaphor or other familiar source of information that the design team is assuming about its users?

The second main point is that though there is some attempt to express this criterion in a measurable fashion, it needs to be done in a way that is specific to the application itself. How is learnability important for an electronic fashion consultant?

 

EXERCISE 7.12 [extra - not in book]

What are the three main categories of usability principle? Choose one of them, and define three principles that are included within it.

answer available for tutors only

Learnability includes

Flexibility includes

Robustness includes

 

EXERCISE 7.13 [extra - not in book]

What is the distinction between usability paradigms and usability principles? What are their advantages and limitations, and why are both important in system design?

answer available for tutors only

Designers have two approaches to developing usable interactive systems, and demonstrating their usability:
1. By example - successful interactive systems that are commonly believed to enhance usability serve as paradigms for the development of future products.
2. More theoretically driven, deriving abstract principles for effective interaction from knowledge of the psychological, computational and sociological aspects of the problem domains. These principles direct the design and evaluation of a product.

Paradigms have been dependent on technological advances and their creative application to enhance interaction. Principles are independent of the technology; they depend more on a deeper understanding of the human element in the interaction.

The problem with paradigms is that they are rarely well defined. It is not clear how they support a user in accomplishing some tasks, so repeated use of some paradigm may not result in the design of a more usable system. Derivation of principles for interaction has usually arisen out of a need to explain why a paradigm is successful and when it might not be. Principles can provide the repeatability which paradigms cannot. But principles alone may be general and abstract definitions which are not very helpful to the designer. The future of interactive system design relies on a complementary approach. The creativity giving rise to new paradigms should be strengthened by the development of a theory which provides principles to support the paradigm in its repeated application.


Individual exercises

ex.7.1 (ans), ex.7.2 (ans), ex.7.3 (open), ex.7.4 (ans), ex.7.5 (ans), ex.7.6 (ans), ex.7.7 (tut), ex.7.8 (tut), ex.7.9 (open), ex.7.10 (tut), ex.7.11 (tut), ex.7.12 (tut), ex.7.13 (tut)

Worked exercises in book

  

Look at some of the principles outlined in this section, and use one or two to provide a usability specification (see Chapter 6, Section 6.3) for an electronic meetings diary or calendar. First identify some of the tasks that would be performed by a user trying to keep track of future meetings, and then complete the usability specification assuming that the electronic system will be replacing a paper-based system. What assumptions do you have to make about the user and the electronic diary in order to create a reasonable usability specification? [page 273]

  

Look up and report back guidelines for the use of colour. Be able to state the empirical psychological evidence which supports the guidelines. Do the guidelines conflict with any other known guidelines? Which principles of interaction do they support? [page 281]


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