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Communications of the ACM

121 - 130 of 2,642 for bentley

Personal vs. commercial content: the similarities between consumer use of photos and music

We describe the results of two ethnographic-style studies that investigated consumer use of photos and music respectively. Although the studies were designed, executed, and analyzed separately, in our findings we discovered striking similarities between the ways in which our participants used personally captured photos and commercially purchased music. These findings have implications for the design of future systems with respect to handling and sharing content in photo or music form. We discuss making allowances for satisficing behavior, sharing media as a way to reminisce or to communicate an experience (tell a story), getting sidetracked while browsing, and similarities in organizing behaviors.

Collect and map it all: the artifact map, a tool for complex context analysis

We have developed the Artifact Map as a tool for context analysis. In a first step, this tool supports and structures the early process of, "hunting for stories" by collecting, describing and mapping all artifacts on a floor map as an anchor. Subsequently, this visible, tangible surrogate paper context is collaboratively extended and used in interviews. Doing so, users are aided in making tacit knowledge explicit, analyzing and reflecting creatively about all aspects of their workaday world. Preparing and working with the Artifact map helps to immerse quickly in a complex context, to find interesting research and design questions, and to establish a common language. Collaborative, social and work processes are jointly sketched on the map, later visually informing further design. Preparing and working with the Artifact Map is both a structured analysis process and an exploratory ethnographic method, with potential to reveal hidden issues that a normal rapid analysis would not disclose. This paper describes the preparation, use, and method in detail. We also report on our results using the Artifact Map to improve our understanding of the context of a vessel traffic center.

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.