The usability of Application Programming Interfaces (APIs) is one of the main factors defining the success of a software based framework. Research in the area of human computer interaction (HCI) currently mainly focuses on end-user usability and only little research has been done regarding the usability of APIs. In this paper, we present a methodology on how to use and combine HCI methods with the goal to evaluate the usability of APIs. The methodology consist of three phasesa heuristic evaluation, a developer workshop and interviews. We setup a case-study according to the methodology, in which we are evaluating the usability of a service-oriented framework API. The goal was to explore different HCI methods and compare the applicability of such methods to find usability problems in an API. The case-study combined qualitative and quantitative methods in order to investigate the usability and intuitiveness of the API itself. It allowed us to identify relevant problem areas for usability related issues that could be mapped to specific types of HCI methods. Examples for this are e.g. structural problems, which are identified mainly in inspection methods, while problems regarding errors and exception handling are mainly identified during the hands-on example part of the developer workshops conducted. The resulting problem areas allow us to develop a first classification of API related usability problems that are making the relevancy of usability issues for APIs more explicit and applicable.

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This paper presents a new predictive scanning strategy based on the N-ary search algorithm. This strategy is demonstrated on three virtual keyboards operated by hissing -a novel interaction method suitable for severely motor impaired people with speech impairments. An experiment with 39 users was conducted to compare the keyboards to three existing scanning keyboards. The participants were able to enter a text by hissing at the speed of 10-16 characters per minute. Experiment results have also shown that a scanning strategy must be predictable for the users as they need to plan their actions in advance.

In this paper, we present an initial study towards of an indoor navigation system for blind people. As the system itself is still in an early stage of development, we conducted a Wizard of Oz study using a generic Wizard of Oz system designed for mobile and ubiquitous studies. The goal of the study was to validate a set of audio-based navigation commands in a field study context. Further, we wanted to identify usability issues of the Wizard of Oz tool, and ensure the appropriateness of the addressed study setup. Therefore, we used eight human wizards as participants in the study. Their task was to guide two blindfolded actors through a predefined route. Such settings helped us to achieve high ecological validity of the results compared to laboratory testing. We found that the developed study setup is fully mobile and can be used in any mobile context, the voice commands chosen for navigation are almost complete, and can be used with slight modifications for the follow-up study. Additionally we identified several usability flaws of the Wizard of Oz tool. After implementing the findings, the tool and the study setup are ready for a follow-up study with blind persons in order to validate the selected voice commands in depth.

In this paper we present a comparative study of free-hand pointing, an absolute remote pointing device. Unimanual and bimanual interaction were tested as well as the static reference system (spatial coordinates are fixed in the space in front of the TV) and novel body-aligned reference system (coordinates are bound to the current position of the user). We conducted a pointand-click experiment with 12 participants. We have identified the preferred interaction areas for left-and right-handed users in terms of hand preference and preferred spatial areas of the interaction. In bimanual interaction, the users relied more on dominant hand, switching hands only when necessary. Even though the remote pointing device was faster than the free-hand pointing, it was less accepted probably due to its low precision.