Managing Quality of Context in Pervasive Computing

1
Managing Quality of Context in Pervasive Computing

• Yingyi Bu, Shaxun Chen, Xianping Tao, Jun Li and
  Jian Lu
• Department of Computer Science Technology,
  Nanjing University

Tao Gu Institute For Infocomm Research,
Singapore
2
Outline

• Introduction
• Related work
• Quality measurement of context
• Context model
• Context Management Mechanism
• Evaluations
• Case Study
• Conclusions

3
Introduction

• Context awareness
• A major software type in pervasive computing
  environment
• Quality of software in pervasive computing
• Quality of program
• Quality of document
• Quality of context

4
Motivating example
Im a context-aware music player, and play Jazz
for you.
Oh, I dont want Jazz now! I want classical music!
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Context Mismatching

• A serious quality issue in current context-aware
  software system
• Context in real world ? context in computers
  view
• What could we do?
• To make context in computers approximate context
  in real world!

6
Related work

• Existing context-aware middleware
• SOCAM (IEEE pervasive computing)
• CoBrA (IEEE internet computing)
• CARISMA (IEEE trans. software engineering)
• Active campus (ICSE 2003)
• MobiPADs (IEEE trans. software engineering)
• .

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Weakness of those systems

• Dont pay enough attention to quality of context.
• In fact, lower quality of context may make users
  unpleasant.

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Work for quality of context

• Dey, et al. gave a novel solution for ambiguity
  resolution by user mediation. (ACM TOCHI)
• Throw the responsibility of maintain quality of
  context to users.

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Work for quality of context

• Xu et, al. established a context consistency
  management mechanism (ESEC/FSE 2005)
• providing a middleware architecture for
  inconsistency detection and resolution

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Work for quality of context

• Xu et, al. proposes an context consistency
  checking mechanism (ICSE 2006)
• Incremental consistency checking

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Our contribution

• Propose quality measures for context
• Establish a formulated context model
• Use ontology based context consistency checking
• Resolve context inconsistency automatically
• Shorten the delay of context delivering

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Quality measures for context

• Delay Time
• the time interval between the time when the
  situation happens in real world and the time when
  the situation is recognized in computers.

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Quality measures for context

• Context Correctness Probability
• The accuracy rate of sensed data
• What is the percent of context correct matching

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Quality measures for context

• Context Consistency Probability
• the probability that contexts in computers are
  consistent
• Dr.Gu in laboratory and Dr.Gu at home are two
  inconsistent contexts
• We use the 3 quality measures as our design
  principles

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Context Model

• Ontology
• a set of shared vocabularies of concepts and the
  interrelationships among these concepts
• Entity
• person, desk, classroom, meeting room, and campus
• Relationship
• the situations or predicates about entities
• Dependency
• the dependent relationship between Relationship

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Example
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Formulate to graph model

• Context graph
• Context
• ER-graph
• Dependency graph
• Context repository
• (see Section4.2 for details)

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Context management mechanism

• Context processing procedure
• Inconsistency resolution in raw context level
• Raw level refactoring in context repository
• Context reasoning and context repository updating

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Context processing procedure
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Inconsistency resolution in raw context level

• Definition Conflict Pair Set
• Conflict pair set, is a set consisting of pairs
  such as (edgea, edgeb), in which corresponding
  contexta(contains edgea) conflicts with
  contextb(contains edgeb).
• Definition Conflict Set
• For a given edge set denoted as EdgeSet, if its
  members conflict with each other, we call EdgeSet
  a conflict set.

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Inconsistency resolution in raw context level

• Definition Relative Frequency-rf
• A formula that calculates the rf value of a
  raw-edge edgei is shown as follow

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RCIR algorithm
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Raw level refactoring in context repository

• Why?
• Before context reasoning, the context repository
  should be updated in order to ensure incorrect or
  outdated high-level contexts are removed.

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RLR algorithm
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Context reasoning and context repository updating

• Use rule reasoning and ontology reasoning orderly
• Update context repository (similar to raw level
  refactoring)

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Evaluations performance study
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Evaluations effectiveness study
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Application Case study

• Smart office scenario

Web Server
Office Room
Meeting Room
show warning
edit slide
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Effect
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Implementations

• We implement 3 versions
• With a simplified quality management (SIR)
• With inconsistency resolution on high level
  contexts (CIR)
• With context management mechanism in this work
  (RCIR)

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Error rate comparison
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Conclusions

• Context quality measures
• Context model
• Context management mechanism
• Evaluations
• Case study

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Future work

• Further improvement on quality of context
• A theoretical model for quality of context

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Reference

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Thank you!