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Are “Usage-Centered” and “Usable” Really the Same Thing?

Isn’t Usage-Centered just another name for Usability or Ease-Of-Use? Not at all! A usage-centered approach to technology and engineering includes usability as an important system quality attribute, but only as one of many important tradeoffs.

Usability asks questions about the user experience:1 can the user complete the task? How readily? How frustrated do users become? How much training do they need? Will users give up and leave your website, return your DVD player, or take back your mobile phone because the user interfaces are just too frustrating? These are all important questions. But they are not the only critical questions.

Usage-centered technology and engineering analyzes systems, processes, workflows, tasks, roles, etc. to determine whether technology can assist or enhance these systems. Early versions of system-enhancing technologies may not be very usable at all. But if a technology provides an important capability—perhaps one that was not even available before—people will put up with some ease-of-use problems. Did early automobile drivers reject cars because they needed a crank to start them? More recently, did early camcorder purchasers decide not to videotape their children because the camera and tape deck combinations were cumbersome and not very user friendly? Even today, people will put up with poorly designed web sites if the alternatives are unavailable or inconvenient.

Usability Follows Capability

Louis Sullivan’s “Form Follows Function”2 philosophy for modernism in architecture in the late 19th century provided an eloquent framework for assessing building designs. We believe a similar framework for usage-centered technology and engineering would read, “Usability Follows Capability.” That is, the first order of business is to consider the value proposition for the technology to ensure that it is capable of answering the critical needs of the stakeholders, knowledge workers, customers, consumers, etc. It makes little sense to look at usability first—or alone—because even a highly usable technology has limited value if it is missing critical functions.

Thus, Usage-Centered Technology and Engineering ensures that we not only build the product correctly, but also build the correct product. You determine the required capabilities through research, analysis, and synthesis based on emerging technologies, innovations, market trends, stakeholder input, task and workflow analysis, testing, feedback, etc.

Building the product correctly requires that critical system quality attributes be identified early, so that they can be incorporated into the fundamental architecture and design of the product. One of these key attributes may be usability. But there are dozens of systems quality attributes, including reliability, security, performance, privacy, adaptability, and maintainability, any of which may or may not be important in providing the needed capability.

Because all these system attributes ultimately affect the user experience, any or all of them may impact usability. For example, products that break easily (poor reliability) or respond too slowly (poor performance) are generally less usable. Security impacts usability as well, although experts disagree about whether higher security requires compromises in usability. But how “usable” is an insecure computer if at some point, the user is hurt by theft of resources, money, identity, etc. And we have ample evidence that security mechanisms with poor usability lead to very insecure behavior (such as simple, easily broken passwords, authentication information taped to computer displays, or even disabled software firewalls "to get my work done").

“Usability Follows Capability” describes an iterative process. Once you know what product to build (the usage-centered paradigm), you can focus on ease of use. However, even the best usability experts do not get it right on the first try (see Works with Quirks is OK!). New capabilities tend to shift the paradigm, and this in turn requires revisions to the human interfaces that provide access to those capabilities.3

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1 One IEEE definition is “The ease with which a user can learn to operate, prepare inputs for, and interpret outputs of a system or components.” Institute of Electrical and Electronics Engineers. IEEE Standard Computer Dictionary: A Compilation of IEEE Standard Computer Glossaries. New York, NY: 1990. ISO defines it as “The extent to which a product can be used by specified users to achieve specified goals with effectiveness, efficiency and satisfaction in a specified context of use.” ISO 9241 – 11 Guidance on Usability Ergonomic Requirements for Office Work and Visual Display Terminals (VDT) 1996.

2 Louis Henri Sullivan, 1856 – 1924 actually said "Form ever follows function." His later work formed the foundation for the ideas of his student, Frank Lloyd Wright.

3 Our goal is to get the usage requirements right first. Some of those requirements can transcend a single product or traditional application. To get the right usage, you may need to "stitch together" applications that were never integrated before. That is why early requirements elicitation is so important for building the correct solution. The European Union's Usability Net site is a good example of this broader systems and software engineering viewpoint, which is becoming more common.


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