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The skyline of a <i>d</i>-dimensional dataset contains the points that are not dominated by any other point on all dimensions. Skyline computation has recently received considerable attention in the database community, especially for progressive methods that can quickly return the initial results without reading the entire database. All the existing… (More)

Given a set of objects <i>P</i> and a query point <i>q,</i> a <i>k</i> nearest neighbor (<i>k</i>-NN) query retrieves the <i>k</i> objects in <i>P</i> that lie closest to <i>q.</i> Even though the problem is well-studied for static datasets, the traditional methods do not extend to highly dynamic environments where multiple continuous queries require… (More)

Given a point q, a reverse k nearest neighbor (RkNN) query retrieves all the data points that have q as one of their k nearest neighbors. Existing methods for processing such queries have at least one of the following deficiencies: (i) they do not support arbitrary values of k (ii) they cannot deal efficiently with database updates, (iii) they are… (More)

— The increasing trend of embedding positioning capabilities (e.g., GPS) in mobile devices facilitates the widespread use of Location Based Services. For such applications to succeed , privacy and confidentiality are essential. Existing privacy-enhancing techniques rely on encryption to safeguard communication channels, and on pseudonyms to protect user… (More)

Among the various types of spatio-temporal queries, the most common ones involve window queries in time. In particular, timestamp (or timeslice) queries retrieve all objects that intersect a window at a specific timestamp. Interval queries include multiple (usually consecutive) timestamps. Although several indexes have been developed for either type,… (More)

In this paper we propose an approach that enables mobile clients to determine the validity of previous queries based on their current locations. In order to make this possible, the server returns in addition to the query result, a <i>validity region</i> around the client's location within which the result remains the same. We focus on two of the most common… (More)

Collaborative Decision Making problems can be addressed through argumentative discourse and collaboration among the users involved. Consensus is achieved through the process of collaboratively considering alternative understandings of the problem, competing interests, priorities and constraints. The application of formal modeling and analysis tools to solve… (More)

A continuous nearest neighbor query retrieves the nearest neighbor (NN) of every point on a line segment (e.g., " find all my nearest gas stations during my route from point s to point e "). The result contains a set of <point, interval> tuples, such that point is the NN of all points in the corresponding interval. Existing methods for continuous nearest… (More)

Recent developments in spatial relations have led to their use in numerous applications involving spatial databases. This paper is concerned with the retrieval of topological relations in Minimum Bounding Rectangle-based data structures. We study the topological information that Minimum Bounding Rectangles convey about the actual objects they enclose, using… (More)

Given two sets of points P and Q, a group nearest neighbor (GNN) query retrieves the point(s) of P with the smallest sum of distances to all points in Q. Consider, for instance, three users at locations q 1 , q 2 and q 3 that want to find a meeting point (e.g., a restaurant); the corresponding query returns the data point p that minimizes the sum of… (More)