This high-level requirement is referred to in ISO software quality standards as “quality in use.” It is determined not only by the ease of use, but also by the extent to which the functional properties and other quality characteristics meet user needs in a specific context of use. ISO 9241-11 (International Organization for Standardization, 1998) defines this as the extent to which a product is effective, efficient, and satisfying in a particular context of use. SOURCE: Adapted from ISO/IEC 25030 (International Organization for Standardization, 2007). A style guide tailored to project needs should form part of the detailed usability requirements.Īt a more strategic level, usability is the extent to which the productįIGURE 7-2 Classification of requirements. Style guides are more precise and are valuable in achieving consistency across screen designs produced by different developers. While designing to conform to guidelines will generally improve an interface, usability guidelines are not sufficiently specific to constitute requirements that can be easily verified. ![]() There are numerous sources of guidance on designing user interface characteristics that achieve these objectives (see the section on guidelines and style guides under usability evaluation). ISO/IEC 9126-1 (International Organization for Standardization, 2001) defines usability in terms of understandability, learnability, operability, and attractiveness. Usability as a product quality characteristic is primarily concerned with ease of use. There are two types of usability requirements. Usability requirements can be seen from two perspectives: characteristics designed into the product and the extent to which the product meets user needs (quality in use requirements). The most recent CHAOS report by the Standish Group (2006), which analyzes the reasons for technology project failure in the United States, found that only 34 percent of projects were successful 15 percent completely failed and 51 percent were only partially successful.įive of the eight (highlighted below) most frequently cited causes of failure were poor user requirements:ĩ.9 percent, unrealistic user expectationsĪmong the main reasons for poor user requirements are (1) an inadequate understanding of the intended users and the context of use, and (2) vague usability requirements, such as “the system must be intuitive to use.”įigure 7-2 shows how usability requirements relate to other system requirements. Inadequate user requirements are a major contributor to project failure. These methods are grouped under design because their major contributions are made in the design phase however, it is important to note that they are also used in defining the context of use and in evaluating design outcomes as part of system operation. As with the descriptions in Chapter 6, each type of method is described in terms of uses, shared representations, contributions to the system design phases, and strengths, limitations, and gaps. The types of methods included here are work domain analysis, workload assessment, situation awareness assessment, participatory design contextual design physical ergonomics methods for analyzing and mitigating fatigue, and the use of prototyping, scenarios, persona, and models and simulations. We begin with a discussion of the need for and the methods used to establish requirements based on the concept of user-centered design. ![]() ![]() ![]() Rather they provide a structure and context in which innovation can take place. The methods are not a substitute for creativity or inventiveness. The methods discussed in this chapter are intended to support identification and exploration of design alternatives to meet the requirements revealed by analyses of opportunity space and context of use. Design is fundamentally an innovative process.
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