Uncertain Range Queries for Necklaces

Abstract

Abstract-We address the problem of efficient processing of spatio-temporal range queries for moving objects whose whereabouts in time are not known exactly. The fundamental question tackled by such queries is, given a spatial region and a temporal interval, retrieve the objects that were inside the region during the given time-interval. As earlier works have demonstrated, when the (location,time) information is uncertain, syntactic constructs are needed to capture the impact of the uncertainty, along with the corresponding processing algorithms. In this work, we focus on the uncertainty model that represents the whereabouts in-between two known locations as a bead, and an uncertain trajectory is represented as a necklace -a sequence of beads. For each syntactic variant of the range query, we present the respective processing algorithms and, in addition, we propose pruning strategies that speed up the generation of the queries' answers. We also present the experimental observations that quantify the benefits of our proposed methodologies.

Probabilistic Range Query over Uncertain Moving Objects in Constrained Two-Dimensional Space

“…model [20], [15], and the necklace uncertainty (NU) model [19], [11]. These models have different assumptions and purposes, but also their own advantages (note: it is a difficult task to say which one is the best).…”

“…data has been proposed [23]. From then on, the probabilistic range query (PRQ) as a variant of the traditional range query has attracted much attentions in the data management community [5], [17], [15], [3], [20], [4], [25], [19]. A well known uncertainty model is using a closed region (in which the object can always be found) together with a probability density function (PDF).…”

Indexing uncertain spatio-temporal data

“…The prevalent approach is to bound the possible positions of an object at each point of time by simple a spatial structure resulting in a spatio-temporal approximation. Examples include static ellipses [25,24,23], dynamic MBRs (Minimum Bounding Rectangles) [15] and dynamic ellipses [22,13] yielding skewed cylinders, diamonds and beads, respectively. To answer queries most of the existing works restrict the possible queries.…”

“…To answer queries most of the existing works restrict the possible queries. Often no specific assumption is made about the probability density function (pdf) of the object positions over time ( [17,25,24,23,22,28,7]). Thus quantifiers such as "always", "sometimes", "definitely" and "possibly" are used to indicate whether an object intersects a given spatio-temporal query window.…”

“…A common method to approximate possible locations between two observations is the beads (or necklace) model ( [11,22]). This model is based on some constraints about the motion of an object.…”