Managing Uncertainty in Sensorbased Applications

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Managing Uncertainty in Sensor-based Applications

• Sunil Prabhakar, Reynold Cheng, Yuni Xia,
• Susanne Hambrusch and Walid Aref
• The PLACE group
• http//www.cs.purdue.edu/place
• Department of Computer Science, Purdue University

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Sensor-based Applications
Database System
sensor
sensor
External Environment e.g., temperature, moving
objects, hazardous materials
Wired/Wireless Network
queries
results
sensor
sensor
user
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Incorrectness of Query Answers
Recorded Temperature
Current Temperature
30
Y1

• Which rooms temperature is between 10oF to 25oF?
• Database Y
• Correct answer X

Y0
20
X1
10
X0
0
oF
X
Y
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Probabilistic Queries
Recorded Temperature
Uncertainty for Current Temperature
30

• Which rooms temp is between 10oF to 25oF?
• (A,10),(B,80)

20
10
0
oF
A
B
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Probabilistic Uncertainty
uncertainty pdf
Li
Ri
uncertainty interval

• Uncertainty Interval pdf
• Can be extended to n dimensions

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Probabilistic Nearest Neighbor
O5

• O1 0.4, O2 0.2,
• O3 0.3, O4 0.1
• Solution only depends on uncertainty interval,
  pdf and cdf

O3
O1
q
O4
O2
O6
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Pruning with x-bounds
left-0.2-bound
right-0.2-bound

• An MBR is not further retrieved if
• Q does not cut left and right x-bounds
• p gt x

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Variance-Based Clustering
cluster of large intervals
yRi
Li
Ri
xy
Q (p 0.75)
(Li,Ri)
variance of Li,Ri
a
b
mean of Li,Ri
cluster of smaller intervals
xLi
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Effect of Query Probability Threshold

• R-tree does not benefit from the increasing value
  of p
• When p is 0.5, Extensive is 4 times better than
  PTI

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Related Publications

• R. Cheng, Y. Xia, S. Prabhakar, R. Shah, and J.
  S. Vitter. Efficient indexing methods for
  probabilistic threshold queries over uncertain
  data. In Proc. of the 26th Intl. Conf. on
  VLDB,2004.
• R. Cheng, D. Kalashnikov, and S. Prabhakar.
  Evaluating probabilistic queries over imprecise
  data. In Proc. of the ACM SIGMOD Intl. Conf. on
  Management of Data, 2003.
• R. Cheng, D. V. Kalashnikov, and S. Prabhakar.
  Querying imprecise data in moving object
  environments. IEEE TKDE, 2004.
• R. Cheng, S. Prabhakar, and D. V. Kalashnikov.
  Querying imprecise data in moving object
  environments. In Proc. of the 19th IEEE ICDE,
  India, 2003.
• R. Cheng and S. Prabhakar. Using Uncertainty to
  Provide Privacy-Preserving and High-Quality
  Location-Based Services. Workshop on Location
  Systems Privacy and Control, Mobile HCI04.