This paper analyzes a Question & Answer site for programmers, Stack Overflow, that dramatically improves on the utility and performance of Q&A systems for technical domains. Over 92% of Stack Overflow questions about expert topics are answered -in a median time of 11 minutes. Using a mixed methods approach that combines statistical data analysis with user interviews, we seek to understand this success. We argue that it is not primarily due to an a priori superior technical design, but also to the high visibility and daily involvement of the design team within the community they serve. This model of continued community leadership presents challenges to both CSCW systems research as well as to attempts to apply the Stack Overflow model to other specialized knowledge domains.

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Sensors are becoming increasingly important in interaction design. Authoring a sensor-based interaction comprises three steps: choosing and connecting the appropriate hardware, creating application logic, and specifying the relationship between sensor values and application logic. Recent research has successfully addressed the first two issues. However, linking sensor input data to application logic remains an exercise in patience and trial-and-error testing for most designers. This paper introduces techniques for authoring sensor-based interactions by demonstration. A combination of direct manipulation and pattern recognition techniques enables designers to control how demonstrated examples are generalized to interaction rules. This approach emphasizes design exploration by enabling very rapid iterative demonstrate-edit-review cycles. This paper describes the manifestation of these techniques in a design tool, Exemplar, and presents evaluations through a first-use lab study and a theoretical analysis using the Cognitive Dimensions of Notation framework.

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Abstract-The Ubicorder is a mobile, location and orientation aware device for browsing and interacting with real-time sensor network data. In addition to browsing data, the Ubicorder also provides a graphical user interface (GUI) that users can use to define inference rules. These inference rules detect sensor data patterns, and translate them to higher-order events. Rules can also be recursively combined to form an expressive and robust vocabulary for detecting real-world phenomena, thus enabling users to script higher level and relevant responses to distributed sensor stimuli. The Ubicorder's mobile, handheld form-factor enables users to easily bring the device to the phenomena of interest, hence simultaneously observe or cause real-world stimuli and manipulate in-situ the event detection rules easily using its graphical interface. In a first-use user study, participants without any prior sensor network experience rated the Ubicorder highly for its usefulness and usability when interacting with a sensor network.

Corruption is endemic in emerging economies, where many transactions of private citizens with government institutions require payment of bribes. The Bribecaster web application enables citizens to report and consume corruption information about dealing with government offices. Bribecaster uses a novel privacy-preserving implicit login schema and one-way hashing for protecting user identities while simultaneously ensuring the accuracy and integrity of reports. This citizen-induced transparency facilitates rational social and individual responses to corruption. Participants in our first-use user study of Bribecaster rated the system highly for its usefulness.