Human-System Integration in the System Development Process A New Look (2007) / Chapter Skim
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7 Defining Requirements and Design
7 Defining Requirements and Design
Pages 189-252
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We begin with a discussion of the need for and the methods used to establish requirements based on the concept of user-centered design. 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.
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• Data describing the results of SA tests • Alertness models • List of the opportunities FIGURE 7-1 Representative methods and sample shared representations for defining requirements and design.
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Style guides are more precise and are valuable in achieving consistency across screen designs produced by different developers. A style guide tailored to project needs should form part of the detailed usability requirements.
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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. In these terms, usability requirements are very closely linked to the success of the product.
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• mean satisfaction score using a questionnaire. Specify Usability Requirements for the New System Define the requirements for the new system, including the type of users, tasks, and working environment.
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The results can be used to prioritize future usability work in subsequent releases. Shared Representations The Common Industry Specification for Usability Requirements (Theofanos, 2006)
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Specification of Requirements When the product requirements are a matter for agreement between the supplier and the customer, the customer organization can specify one or more of the following: • intended context of use, • user performance and satisfaction criteria, and • test procedure. The Common Industry Specification for Usability Requirements provides a baseline against which compliance can be measured.
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HUMAN-SYSTEM INTEGRATION IN SYSTEM DEVELOPMENT Contributions to System Design Phases Usability requirements should be integrated with other systems engineering activities. For example, the ISO/IEC 15288 standard (International Organization for Standardization, 2002)
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. WORK DOMAIN ANALYSIS Overview Among the questions that arise when facing the design of a new system are the following: What functions will need to be accomplished?
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. Work domain analysis methods grew out of an effort to design safer and more reliable nuclear power plants (Rasmussen, 1986; Rasmussen, Pejtersen, and Goodstein, 1994)
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A prominent example is cognitive work analysis (Rasmussen, 1986; Rasmussen et al., 1994; Vicente, 1999) that uses work domain analysis as the foundation for deriving implications for system design and related aspects of human-system integration, including function allocation, display design, team and organization design, and knowledge and skill training requirements.
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FIGURE 7-3 Selected portions of a work domain representation for a pressurized water reactor nuclear power plant.
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The output of a work domain analysis is used to inform further analyses that feed different elements of human-system integration. Table 7-1 provides a summary of the major elements of a cognitive work analysis that provide traceable links between the results of the work domain analysis and implications for system design, including function allocation decisions, team and organization design, design of physical and information systems including displays, personnel selection and training, development of procedures, specification of test cases to drive system evaluation, and conduct of human reliability analyses as part of risk-based analyses.
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to foster understanding and reduce workload. Use of Work Domain Analysis in the Port Security Case Study Work domain analysis has been an integral part of the port security HSI work described in Chapter 5.
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The content and organization of the group view display was based on a work domain analysis (see Figure 7-4)
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FIGURE 7-4 Schematic representation of a wall-mounted group view display for a compact power plant control room derived from a cognitive work analysis approach.
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that are needed to effectively support performance in the domain. The application of work domain analysis throughout the HSI design cycle has been successfully illustrated by Neelam Nakar and her colleagues, who have been applying work domain analysis and cognitive work analysis methods to the design of a first-of-a-kind Australian AWACS-style air defense platform called the Airborne Early Warning and Control (Naikar and Sanderson, 1999, 2001; Naikar et al., 2003; Naikar and Saunders, 2003; Sanderson et al., 1999; Sanderson, 2003)
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A related strength of work domain analysis methods is that it encourages explicit links between analysis and design via intermediate design artifacts. As the design evolves, these artifacts can be expanded and modified to provide a tracable link between domain demands, cognitive and performance requirements, and system features intended to provide the requisite support.
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For tasks involving significant physical effort, physical workload is an ergonomic issue and in sustained task performance is usually measured in terms of oxygen consumption, or heart rate. Prediction of physical workload depends on having measurement results from other related activities and conditions and estimating the differences between the known results and the postulated activity.
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Then, after making corresponding estimates of the time required for each task element in context, they used task analysis results to bring together the elemental components into estimates of the aggregate loads as a function of time on each modality. This basic approach has also been used in a variety of modeling contexts, including network models and more detailed human performance simulations (Laughery and Corker, 1997)
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. These shared representations illustrate the timelines of activities, showing where overlaps occur, with highlights showing phases in which the workload exceeds limits.
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There is a need for more collaboration among the specialists of the manpower, personnel, and human factors domains to ensure that the studies that are undertaken meet the requirements of all these stakeholders. Suitable shared representations are not well developed.
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. Methods and Shared Representations Scenarios The analysis phases of scenario-based methods are noted in the previous chapter (Carroll, 1995, 2000; Carroll, Rosson, and Carroll, 2002b, 2003)
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However, by using the materials for usability testing, these approaches effectively reduce the user's input into an acceptance test. In participatory design, the goal is for the users to contribute as peer co-designers, not simply as evaluators.
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. The specific methods used by ethnographers in design activities tend to invoke other methods, previously described in the section on participatory design.
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Contributions to the System Design Process Each participatory design method produces its own characteristic shared representation and contribution; several of these were reviewed in the preceding chapter on analysis. Table 7-2 provides a summary of contributions and shared representations.
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Strengths, Limitations, and Gaps Strengths and weaknesses of participatory design are similar to those for participatory analysis, as discussed in Chapter 6. A principal strength of the participatory approaches is the collection and use of detailed, in-depth information from the users' perspective.
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. CONTEXTUAL DESIGN In the participatory analysis section of Chapter 6, we summarized the contextual inquiry process, including the three activities of contextual inquiry, interpretation, and affinity analysis, as well as the construction of the five models characterized, respectively, in flow, sequence, physical, cultural, and artifact terms.
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, and the structure and function clustering is one of the principal outcomes of a requirements analysis, to assist other systems professionals in making choices in function allocation. Shared Representations Contextual design is intended to produce formal requirements and specifications.
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. Shared Representations Shared representations range from physiological tests, such as the measurement of systolic blood pressure, to subjective instruments, such as ratings of perceived exertions (Louhevaara et al., 1998)
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Finally, methods to assess physical risk also tend to rely on shared representations that are at least partially subjective -- typically taking the form of checklists and rating scales. With respect to human digital modeling, an avatar or virtual human with specific population attributes is rendered as it dynamically performs tasks in a system.
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Methods that attempt to quantify effort and fatigue include the Borg Ratings of Perceived Exertion scale and the Muscle Fatigue Assessment method (Hedge, 2005)
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Human Digital Modeling Digital human models are ergonomic analysis and design tools that are intended to be used early in the product and system development process to improve the physical design of systems and workstations (Chaffin, 2004, 2005)
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The methods can be applied at the task or system level. To the extent that systems require physical activity, physical ergonomics methods are applicable for defining solutions -- that is, to support identification and exploration of design alternatives.
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Another gap that is slowly being filled is better integration among physical, cognitive, and macroergonomic approaches in order to consider total human-system integration. In terms of newer methods, such as human digital modeling, current digital human models are generally static or are not fully dynamic, integrated models.
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Achieving situation awareness has therefore become a design criterion in addition to more traditional performance measures. However, measuring situation awareness requires more than an everyday understanding of the term.
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Data describing the results of situation awareness tests provide useful shared representation with other stakeholders, because it is a concept that, in its everyday meaning, can be widely understood as important to good performance. Strengths, Limitations, and Gaps In contrast to overall system performance measures, situation awareness measures provide indices of the way the system is influencing human performance per se, and therefore it is able to provide clues to how to improve the design from the perspective of the user.
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A significant gap is that one would like to be able to predict situation awareness before anything is built, but good predictive models to assess it are not available, although efforts are under way. METHODS FOR MITIGATING FATIGUE Overview Systems manned by operators need to accommodate the inherent limitations imposed by human circadian rhythms and endurance capacities.
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Given the potentially lethal impact of fatigue on the job, application of these principles and methods during system design is warranted. The principal risk reduction associated with application of these methods is that of operations, which will lead to excessive fatigue and corresponding degradations in human performance.
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They are now beginning to reserve certain blocks of rooms and floors for day sleepers and to implement other measures, such as blackout shades and additional soundproofing. Shared Representations Alertness design methods have a common shared representation in specifying the impact on operator sleep.
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More involved methods, such as nap period design or sleep environment planning, can enhance alertness during long assignments or unusual shift rotations. A primary limitation of alertness design methods is that they are relatively unknown outside the fatigue research and transportation community.
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Some design representation methods emphasize the delivery of a formal, integrated concept, embodied in the form of a highly produced and convincing story. By contrast, some participatory analysis methods focus on storytelling to create a level playing field, so as to put users and technologists on a common footing, making scenarios useful as shared representations.
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. Shared Representations There are a variety of shared representations that can result from building scenarios.
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Scenarios can be simultaneously implicit and explicit. Contributions to System Design Phases Scenarios can be used in the very early stages of the design process to help explain possible system behavior.
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Shared Representations While scenarios are concise narrative descriptions, personas are descriptions of one or more people who are (or will be) using a product to achieve specific goals.
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Contributions to the System Design Process There is little formal research to support the creation of personas as a part of the systems design process. Less formal reports from practitioners are overwhelmingly positive (e.g., Cooper, 2004; Pruitt and Adlin, 2006; Adlin et al., 2006)
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of each type of user, and it can be used further for a high-level quantification of the impact of each feature decision on each class of users and thus on the likely overall success of the product. PROTOTYPING Overview Prototyping is a method that can be used at any time during the design process.
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Figure 7-6 shows some examples of different types of prototypes. Shared Representations The shared representations produced as output from prototyping may take a variety of forms (Beaudouin-Lafon and Mackay, 2003; Houde and Hill, 1997)
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7-6 are produced so powerful as shared representations is that they are tangible and can easily be shared and foster communication among team members, stakeholders, and end-users. Prototypes function to make explicit an aspect of form, fit, or functionality (Boland and Collopy, 2004)
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or a paper-and-pencil mock-up of a user interface (e.g., Ehn and Kyng, 1991; Muller, 2001; Muller et al., 1995) ; in some cases, the prototype is designed to be modifiable only by experts while in other cases the prototype is designed to be modifiable by anyone, including actual or potential users of the eventual product or system (e.g., Ehn and Kyng, 1991; Muller, 2001; Muller et al., 1994, 1995; Sanders, 2000)
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DEFINING REQUIREMENTS AND DESIGN prototypes are so real, they make the experience of the product, application, or service so tangible that they can influence teams to fix too quickly on a potential solution. When that happens, people are usually taken in by the level of finish in the prototype and believe that all the qualities and features are set -- rather than being open to change.
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They can reduce the time and data gathering required for functional evaluation by screening alternatives and identifying the critical parameter ranges to test. They can also be used for decision making about specifications or the most promising design alternatives.
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For example, NASA has used simulation in its role in research to support the continued improvement and the reduction of human error in the National Aerospace System. They have employed everything from single crew member part-task simulations to full-mission representations of the coordinated behavior of commercial aircraft crews and air traffic controllers in air operations.
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. These models can be applied as soon as there is an explicit design for a user interface, and they have been used to predict response times, learning times, workload, and to provide a measure of interface consistency and complexity (i.e., similar tasks should use similar methods and operators)
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Digital Human Physical Simulations A third class of models is anthropometric representations of the size, shape, range of motion, and biomechanics of the human body (see also the section on physical ergonomics)
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The resulting models and analyses can be shared between designers and across design phases. Having a concrete computer mannequin that confirms the success or failure of accommodation at a workplace is a very useful shared representation.
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. These human behavior representations are more detailed because they actually mimic the information processing activities that generate behavior.
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Analysis and network models will be particularly helpful in this stage because they are more flexible and can be performed earlier in the design process. In many cases, the model's impact in the elaboration phase may be derived from design lessons learned from previous designs -- they will help the designer choose better designs in what can be a very volatile design period.
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When the design has progressed to the point at which concrete prototype simulations can be developed, it can be very useful to exercise the simulation with a human behavior representation. The development of the human behavior representation itself will be illuminating because it will make the tasks and human performance concrete, but it will also be useful for exploring alternative operational concepts, refining the procedures of use, and identifying the user interface requirements.
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Strengths, Limitations, and Gaps Strengths Simulations, particularly human-in-the-loop simulations, and humansystem models are especially valuable because they make concrete, explicit, and quantitative the role of users in task execution and their impact on the characteristics of the systems to be controlled. They provide concrete examples of how a system will operate, not only how the equipment will operate, but also what human-system performance will result.
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In order for human-system models to be credible as shared representations, they must make their characteristics and predictions explicit in a way that can be understood by the range of stakeholders for whom they are relevant. There is a range of questions that people ask about models including what their structure is, how they "work," and why they did or did not take a particular action (Councill, Haynes, and Ritter, 2003)
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There are gaps in integrating user models within and across design phases as well as connecting them to the systems themselves. As models get used in more steps in the design process, they will serve as boundary objects, representing shared understanding about users' performance in the systems under evaluation -- their goals, their capabilities to execute tasks, and their behavior.
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. In the long term, we think that the approach of having models of human behavior representations interacting directly with an unmodified or instrumented interface software will become the dominant design approach, which can also include automatic testing with explicit models.
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For example, there is a forthcoming National Academies study on organizational models (National Research Council, 2007) and there is also recent work on including social knowledge in models of human behavior representation (e.g., Sun, 2006)
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