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UNIT- I Usability of Interactive Systems- Introduction New technologies provide extraordinary-almost supernatural-powers to those people who master them. Networked computers with advanced interfaces are compelling new technologies that are being rapidly disseminated. Great excitement spreads as designers provide remarkable functions in carefully crafted interactive devices and interfaces. The opportunities for rule-breaking innovators and business-focused entrepreneurs are substantial, and the impacts on individuals, organizations, and cultures are profound. Like early photography equipment or automobiles, early computers were usable only by people who devoted effort to mastering the technology. Harnessing the computer's power is a task for designers who combine an understanding of technology with a sensitivity to human capacities and needs. User interfaces help produce business success stories and Wall Street sensations.They also produce intense competition, copyright-infringement suits,intellectual-property battles, mega-mergers, and international partnerships. Crusading Internet visionaries promote a world with free access to music,while equally devoted protectors of creative artists argue for fair payments. User interfaces are also controversial because of their central role in national identification schemes, homeland defense, crime fighting, medical records management, and so on. In the aftermath of the September 11, 2001 terrorist attacks, some members of the U.s. Congress blamed the inadequacies of user interfaces for the failure to detect the terrorists. At an individual level, user interfaces change many people's lives: effective user interfaces for professionals mean that doctors can make more accurate diagnoses and pilots can fly airplanes more safely; at the same time, children can learn more effectively and graphic artists can explore creative possibilities more fluidly. Some changes, however, are disruptive. Too often, users must cope with frustration, fear, and failure when they encounter excessively complex menus, incomprehensible terminology, or chaotic navigation paths. What user wouldn't be disturbed by receiving a message such as "Illegal Memory Exception: Severe Failure" with no guidance about what to do next?

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Usability goals and measures Usability goals: 1. Ascertain the users' needs. 2. Ensure proper reliability. 3. Promote appropriate standardization, integration, consistency and portability. 4. Complete projects on schedule and within budget. Standardization refers to common user-interface features across multiple applications. Apple Computers 0992, 2002) successfully developed an early standard that was widely applied by thousands of developers, enabling users to learn multiple applications quickly. When the Microsoft Windows 0999, 2001) interface became standardized, it became a powerful force. Similarly, the standards provided by the World Wide Web Consortium have done much to accelerate adoption of the Web. Integration across application packages and software tools was one of the key design principles of Unix. (Portability across hardware platforms was another.) If file formats are used consistently, users can apply multiple applications to transform, refine, or validate their data. Consistency primarily refers to common action sequences, terms, units, layouts, colors, typography, and so on within an application program. Consistency is a strong determinant of success of interfaces. It is naturally extended to include compatibility across application programs and compatibility with paper or non-computer-based systems. Portability refers to the potential to convert data and to share user interfaces across multiple software and hardware environments. The fourth goal for interface designers is to complete projects on schedule and within budget. Proper attention to usability principles and rigorous testing often lead to reduced cost and rapid development Usability Measures: If adequate requirements are chosen, reliability is ensured, standardization is addressed, and scheduling and budgetary planning are complete, developer can focus their attention on the design and testing process. Multiple design alternatives must be evaluated for specific user communities and for specific benchmark tasks. A clever design for one community of users may

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be inappropriate for another community. An efficient design for one class of tasks may be inefficient for another class. 1. Time to learn. How long does it take for typical members of the user community to learn how to use the actions relevant to a set of tasks? 2. Speed of performance. How long does it take to carry out the benchmark tasks? 3. Rate of errors by users. How many and what kinds of errors do people make in carrying out the benchmark tasks? Although time to make and correct errors might be incorporated into the speed of performance, error handling is sucha critical component of interface usage that it deserves extensive study 4. Retention over time. How well do users maintain their knowledge after an hour, a day, or a week?Retention may be linked closely to time to learn, and frequency of use plays an important role. 5. Subjective satisfaction. How much did users like using various aspects of the interface? The answer can be ascertained by interview or by written (Usability motivations) The enormous interest in interface usability arises from the growing recognition of how poorly designed many current interfaces are and of the benefits elegant interfaces bring to users. This increased motivation emanates from developers of life-critical systems; industrial and commercial systems; office, home, and entertainment applications; exploratory, creative, and collaborative interfaces; and socio technical systems. Life-critical systems Life-critical systems include those that control air traffic, nuclear reactors, power utilities, police or fire dispatch, military operations, and medical instruments. In these applications high costs are expected, but they should yield high reliability and effectiveness. Industrial and commercial uses Typical industrial and commercial uses include banking, insurance, order entry, inventory management, airline and hotel reservations (Fig. 1.8), car rentals, utility billing, creditcard management, and point-of-sales terminals. In these cases, costs shape many judgments.Operator training time is expensive, so ease of learning is important. Since many businesses are international, translation to multiple languages and adaptations to local cultures are necessary. Office, home, and entertainment applications The rapid expansion of office, home, and entertainment applications is the third source of interest in usability. Personal-computing applications include e-mail, bank machines,

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games (Fig. 1.9), educational packages, search engines, cell phones, and mobile devices.For these interfaces, ease of learning, low error rates, and subjective satisfaction are paramount because use is frequently discretionary and competition is fierce. If the users cannot succeed quickly, they will abandon the use of a computer or try a competing package. In cases where use is intermittent, clear, easy-to-remember procedures are important, and if retention is still faulty, comprehensible online help becomes important. Exploratory, creative, and collaborative interfaces An increasing fraction of computer use is dedicated to supporting human intellectual and creative enterprises. Exploratory applications include World Wide Web browsing search engines, scientific simulation, and business decision making. Creative environments include writing work benches, architectural design systems Sociotechnical systems A growing domain for usability is in complex systems that involve many people over long time periods, such as systems for voting, health support, identity verification, and crime reporting. (Universal usability) Universal usability refers to the design of information and communications products and services that are usable for every citizen. The concept has been advocated by Professor Ben Shneiderman, a computer scientist at the Human-Computer Interaction Lab at the University of Maryland, College Park. Variations in physical abilities and physical workplaces These physical abilities influence elements of the interactive-system design. They also play a prominent role in the design of the workplace or workstation (or play station). The draft standard Human Factors Engineering of Computer Workstations (2002) lists these concerns:  work-surface and display-support height • Clearance under work surface for legs • Work-surface -width and depth • Adjustability of heights and angles for chairs and work surfaces • Posture-seating depth and angle; back-rest height and lumbar support • Availability of armrests, footrests, and palm rests • use of characteristic. Diverse cognitive and perceptual abilities •Short-term and working memory

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