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Query Answering on Trajectory Cuboids using PrimeNumbers Encodings
Elio MasciariICAR-CNR
IDEAS ConferenceLisbon September2011
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Outline
Trajectory DataPrime Numbers Encoding for PathsWarehousing StepsExperimental EvaluationConclusions
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Trajectory Data
Data Pertaining to time and position of moving objects◦GPS systems◦Traffic management
Two dimensional ◦In general partitioning is a well accepted
solution Segmentation Regioning
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Trajectory Data
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Our Solution: Regioning+ Encoding
Regioning◦IPCA: Identifies Preferred Directions for Data◦Differential Regioning
Prime Number Encoding:◦Trajectories represented as products of prime
numbers
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Regioning: regions close to principal directions are finer
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Encoding: prime numbers
T1 = ABC crossing three regions A,B,C. Assign to regions A, B and C respectively the prime numbers 3,5,7
For trajectory T1 the witness W1 is 52 since 52%3 = 1 = pos(A) and 52%5 = 2 = pos(B) and 52%7 = 3 = pos(C)
Store the encoded trajectories using a binary tree
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Trajectory Warehousing
Building Specialized cuboids:TRAC◦Distinct Count Problem
Measures◦the number of distinct trajectories
(Intersections), ◦the average traveled distance (Distance), ◦the average time interval duration (Duration)
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TRACs
Precomputed cuboids pertaining to most interesting recent data
Merging cuboids at different granularity levels when needed
Iceberg assumption
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Performances
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Performances
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Performances
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Performances
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Conclusions
Data reduction by regioningEfficient Queying via EncodingWarehousing in order to allow trajectory
querying effectivelyGood performances
◦Accuracy◦Efficiency