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Chapter 3. Deconstructing the Problem: P... > Living With a Model: What the Model ...

Living With a Model: What the Model Implies About Design Priorities, Resources, and Feedback

This model of a complete user interface is useful because it provides a common method and vocabulary for deconstructing the aspects of an interface, for prioritizing design tasks, for allocating design resources, and for interpreting user feedback. As shown in Figure 3.3, the order of the layers follows three distinct axes.

Figure 3.3. By adding the three axes to the bottom of the diagram, the implications for prioritizing and ordering design tasks are clear.

Technical Flexibility. Because the structural layers describe the fundamental qualities and workings of the interface, they often have some representation in the architecture and functioning of the software code. This is especially true for the conceptual model. For example, after a team starts to think of an application as “a mail system,” it is very difficult not to let that concept seep into the code. As a result, modifying the structural aspects of the interface requires the most engineering effort. By contrast, it is relatively easy to modify the Presentation tier because those elements can be isolated in the code with cascading style sheets, for example.

User Awareness. Because users can literally see the elements of the presentation layers, they are highly aware of them. By contrast, users can “see” the behavioral layers only by interacting with the interface and the structural layers. And they do this by developing an understanding of the interface. As a result, most user comments focus on the Presentation tier, with correspondingly fewer comments about the Behavior and Structure tiers.

Impact on Usability. Paradoxically, the elements that users are least aware of are the very ones that tend to have the deepest impact on usability. And vice versa, the elements that are foremost in a user’s mind are often a distraction from the more fundamental concerns of the lower layers. For example, although a striking visual design might help distract attention and resources away from a poor conceptual model, it can’t fix the problem any more than a movie’s music, lighting, or special effects can fix a poorly conceived story.

The message contained in these three axes is clear: Although the foundational components, such as the conceptual, structural, and organizational models, are the elements that users comment on least often, they not only have the most impact on users’ understanding and success, but also require the most engineering effort to change. As a result, if there are time or resource constraints on the design of a new product, the priority should be on the lower layers of the interface with particular attention to the conceptual model. Similarly, if the design is for additions or enhancements to an existing product, the effort can focus more on the behavioral and presentation aspects because the structural aspects are already in place.

In addition to prioritization, the order of the layers suggests how to interpret the frequency of certain types of user comments as well as how to rate their severity and impact on engineering resources. For example, because users are most aware of the Presentation tier, comments about color, layout, and imagery should be expected. Fortunately, even if the comments are heard repeatedly, the presentation aspects of the interface do not have a major effect on usability and can be altered later with minimal impact on engineering.

Similarly, although users might be struggling to understand a product’s basic purpose and operation, they will never attribute it to the conceptual model. If a designer or researcher concludes that there is a problem with the conceptual model, however, addressing the issue immediately is imperative because its detrimental effect on usability will reverberate throughout other layers of the interface, and each additional line of code increases the engineering effort required to change it.

A final way to apply the model to real-world design problems is to alter the diagram to reflect the complexity of an interface. By altering the width of each layer, the relative complexity and simplicity of each component of an interface can be easily understood. This understanding can then be used to allocate design skills, resources, and time. Figures 3.4 through 3.7 illustrate the model applied to three different Web applications and one content-based Web site.

Figure 3.4. Like other newspaper sites, the large volume of written content at washingtonpost.com requires a sophisticated organizational model, navigational system, and set of text labels.

Figure 3.5. The interface for the online gift store Red Envelope reflects a limited need for editing and manipulation behaviors, and a focus on visual presentation.

Figure 3.6. The interface for online services such as Hotmail typically requires a complex Behavior tier with a relatively limited organizational model.

Figure 3.7. Like other travel sites, JetBlue has limited viewing and navigational functions. However, the number of steps necessary to make a reservation requires complex editing and manipulation behaviors.

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