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Communications of the ACM

121 - 130 of 2,588 for bentley

Bannerbattle: introducing crowd experience to interaction design

We introduce crowd experience as an emergent field in interaction design research. Crowds as social phenomena are already well-established as a research theme in sociology and social psychology. However, the understanding of crowds as users of technology is so far unexplored. Based on the existing literature on crowd behavior, we identify three distinct qualities of crowd experience, which we introduce to interaction design: imitation, emergence, and self-organization. These three qualities informed the design of the research prototype, BannerBattle, which is an interactive display to support crowd experiences at football stadiums. Based on findings in the case study, we discuss how crowd theory complements and challenges existing experience-centered design approaches. We suggest that crowd theory is an important resource when designing technology to support crowd experiences. Moreover, a focus on crowd experience may nuance and expand the already well-established field of experience-centered design research.

Close pair queries in moving object databases

Databases of moving objects are important for air traffic control, ground traffic, and battlefield configurations. We introduce the (historical and spatial) range close-pair query for moving objects as an important problem for such databases. The purpose of a range close-pair query for moving objects is to find pairs of objects that were closer than ε during time interval $I$ and within spatial range R, where ε, I and R are user-specified parameters.This paper solves the range close-pair query using two components: the retrieval component and the close-pair identification component. The retrieval component breaks up long trajectories into trajectory segments, which are produced in increasing time order, without the need for sorting. The retrieval component takes advantage of a new index mechanism, the Multiple TSB-tree. The segments are then pipelined to the close-pair identification component. The identification component introduces a novel spatial sweep that sweeps by time and one spatial dimension at the same time. Extensive experimental results are provided, demonstrating the advantages of the new approach when considering close pairs.

A space-optimal data-stream algorithm for coresets in the plane

Given a point set P⊆R2, a subset Q⊆ P is an ε-kernel of P if for every slab W containing Q, the (1+ε)-expansion of W also contains P. We present a data-stream algorithm for maintaining an ε-kernel of a stream of points in R2 that uses O(1/√ ε) space and takes O(log (1/ε)) amortized time to process each point. This is the first space-optimal data-stream algorithm for this problem.

Robust and efficient polygon overlay on parallel stream processors

The plane sweep algorithm, although widely used in computational geometry, does not parallelize efficiently, rendering it incapable of benefiting from recent trends of multi-core CPUs and general-purpose GPUs. Instead of the plane sweep, some researchers have proposed the uniform grid as a foundation for parallel algorithms of computational geometry, but long-standing robustness and performance issues have deterred its wider adoption, at least in the case of overlay analysis. To remedy that, we have developed previously missing methods to perform snap rounding and compute efficiently the winding number of overlay faces on the uniform grid, and we have implemented them as part of an extensible geometry engine to perform polygon overlay with OpenMP on CPUs and CUDA on GPUs. The overall algorithm works on any polygon configuration, either degenerate, overlapping, self-overlapping, disjoint, or with holes. On typical data, it features time and space complexities of O(N + K) where N is the number of edges and K the number of intersections. Its single-threaded performance not only rivals the plane sweep, it achieves a parallel efficiency of 0.9 on our quad-core CPU, with an additional speedup of over 4 on our GPU, a result that should extrapolate to distributed computing and other geometric operations.

The coordinative functions of flight strips: air traffic control work revisited

Cooperation in time-critical and physically distributed work settings, such as air traffic control, requires extensive coordination between the involved actors. For this coordination to be efficient the controllers rely both on the comprehensive use of rules and procedures, and on artifacts supporting them in following these procedures. At the Copenhagen Air Traffic Control Center this coordination is largely carried out through the use of a flight plan database system, paper flight strips, and a closed-circuit television system. In relation to the introduction of a new and increasingly automated system in the year 2003 this paper discusses the coordinative functions served by these three, soon to be replaced, artifacts from a design perspective. Despite the skepticism expressed in previous research, our results show that a further computerization could be successful if the coordinative functions the system currently fulfills are properly preserved.

Personal knowledge questions for fallback authentication: security questions in the era of Facebook

Security questions (or challenge questions) are commonly used to authenticate users who have lost their passwords. We examined the password retrieval mechanisms for a number of personal banking websites, and found that many of them rely in part on security questions with serious usability and security weaknesses. We discuss patterns in the security questions we observed. We argue that today's personal security questions owe their strength to the hardness of an information-retrieval problem. However, as personal information becomes ubiquitously available online, the hardness of this problem, and security provided by such questions, will likely diminish over time. We supplement our survey of bank security questions with a small user study that supplies some context for how such questions are used in practice.

BSkyTree: scalable skyline computation using a balanced pivot selection

Skyline queries have gained a lot of attention for multi-criteria analysis in large-scale datasets. While existing skyline algorithms have focused mostly on exploiting data dominance to achieve efficiency, we propose that data incomparability should be treated as another key factor in optimizing skyline computation. Specifically, to optimize both factors, we first identify common modules shared by existing non-index skyline algorithms, and then analyze them to develop a cost model to guide a balanced pivot point selection. Based on the cost model, we lastly implement our balanced pivot selection in two algorithms, BSkyTree-S and BSkyTree-P, treating both dominance and incomparability as key factors. Our experimental results demonstrate that proposed algorithms outperform state-of-the-art skyline algorithms up to two orders of magnitude.

An experimental investigation of set intersection algorithms for text searching

The intersection of large ordered sets is a common problem in the context of the evaluation of boolean queries to a search engine. In this article, we propose several improved algorithms for computing the intersection of sorted arrays, and in particular for searching sorted arrays in the intersection context. We perform an experimental comparison with the algorithms from the previous studies from Demaine, López-Ortiz, and Munro [ALENEX 2001] and from Baeza-Yates and Salinger [SPIRE 2005]; in addition, we implement and test the intersection algorithm from Barbay and Kenyon [SODA 2002] and its randomized variant [SAGA 2003]. We consider both the random data set from Baeza-Yates and Salinger, the Google queries used by Demaine et al., a corpus provided by Google, and a larger corpus from the TREC Terabyte 2006 efficiency query stream, along with its own query log. We measure the performance both in terms of the number of comparisons and searches performed, and in terms of the CPU time on two different architectures. Our results confirm or improve the results from both previous studies in their respective context (comparison model on real data, and CPU measures on random data) and extend them to new contexts. In particular, we show that value-based search algorithms perform well in posting lists in terms of the number of comparisons performed.

Adding an interactive display to a public basketball hoop can motivate players and foster community

Interactive displays that aim to engage people through play have been successfully deployed in urban environments. However, there has been little work bringing interactive displays into existing public game spaces like outdoor basketball courts. To explore this, we designed an interactive display for a public half-court basketball hoop. We studied the impact of 3 different display modes over a 10-week period through interviews with players, spectators, and passers-by. Our findings suggest 3 dimensions for the design space of such interactive displays: balancing noticeability across different user groups, support for different play action, and support for connecting user groups. We also present 6 design tactics along these dimensions to help designers create engaging interactive displays for public game spaces. using it to facilitate engaging playful experiences.

Social audio features for advanced music retrieval interfaces

The size of personal music collections has constantly increased over the past years. As a result, the traditional metadata based lists to browse these collections have reached their limits. Interfaces that are based on music similarity offer an alternative and thus are increasingly gaining attention. Music similarity is typically either derived from audio-features (objective approach) or from user driven information sources, such as collaborative filtering or social tags (subjective approach). Studies show that the latter techniques outperform audio-based approaches when it comes to describe the perceived music similarity. However, subjective approaches typically only define pairwise relations as opposed to the global notion of similarity given by audio-feature spaces. Many of the proposed interfaces for similarity based music access inherently depend on this global notion and are thus not applicable to user driven music similarity measures. The first contribution of this paper is a high dimensional music space that is based on user driven similarity measures. It combines the advantages of audio-feature spaces (global view) with the advantages of subjective sources that better reflect the users' perception. The proposed space compactly represents similarity and therefore is well suited for offline use, such as in mobile applications. To demonstrate the practical applicability, the second contribution is a comprehensive mobile music player that incorporates several smart interfaces to access the user's music collection. Based on this application, we finally present a large-scale user study that underlines the benefits of the introduced interfaces and shows their great user acceptance.