Historically, usability was associated with the user interface, and humancomputer interaction (HCI) professionals concentrated their work here. This makes perfect sense, because most of our understanding of a given system and its usability is shaped by the user interface.
But usability is much deeper than the user interface. In my view, it relates to the complex choices that users of the system make to accomplish one or more tasks easily, efficiently , enjoyably, and with a minimum of errors. Many, although not all, of these choices are directly influenced by your tarchitecture . In other words, if your system is perceived as "usable," it will be usable because it was fundamentally architected that way.
This view of usability makes certain demands on marketects and tarchitects. For different reasons, both must understand users and the context in which they work. The marketect needs these data to ensure that the system is providing a competitive edge, that it is meeting users' most important needs, and that it is providing the necessary foundation for a long- term relationship. The tarchitect needs these data to create the deeper capabilitiesfrom performance to internationalizationthat result in usable systems.
As a trivial example, consider users in different domains. An application designed to help a biochemist manage the vast amount of data created by automated experiment equipment is vastly different from the airport self-service kiosk where I obtain a boarding pass before taking a flight. A clear understanding of what makes these systems usable can only be acquired by understanding representative users and the context in which they work. The marketect needs to understand the use cases associated with user goals and motivations, how creating these systems will serve user needs, and so forth. The tarchitect must also understand the uses cases associated with these systems, even though the technology that underlies each solution is radically different.
More subtly, understanding users and the context in which they work is important for the quantitative and qualitative dimensions of usability. Quantitative aspects of usability address such things as performance and data entry error rates. Qualitative aspects address such things as satisfaction and learnability. Because no application can maximize every possible quantitative or qualitative value, tradeoffs must be made. Good tradeoffs produce usable applications and winning solutions.
There are a variety of techniques you can use to gain an understanding of users, including observation, interviews, questionnaires, and direct experience. The last is one of my favorites, a technique I refer to as experiential requirements. Simply put, perform the tasks of your users as best you can to understand how to create a system they find usable. This approach isn't appropriate for all situations (e.g., surgery or auto racing), but it is one of the best for many.
The fundamental, almost overpowering, reason to create usable systems is money. A large amount of compelling data indicates that usability pays for itself quickly over the life of the product. Whereas a detailed summary of the economic impact of usability is beyond the scope of this book, I will mention one system I worked on that was used by one of the world's largest online retailers. A single phone call to customer support could have destroyed the profits of a dozen or more successful transactions, so usability was paramount. Other applications may not be quite as sensitive to usability, but my experience demonstrates that marketects and tarchitects routinely underestimate usability's importance. Benefits of usable systems include any or all of the following, each of which can be quantified .
It is generally not possible to achieve every possible benefit of usability simultaneously . For example, a system that is easy to learn for novices is likely to be far too slow for experts. Because of this, it is vital that marketects and tarchitects work together to ensure that the correct aspects of usability are being emphasized in the project.