A service-oriented middleware for building
context-aware services
Tao Gu, Hung Keng Pung, Da Qing Zhang
Institute for Infocomm Research, Singapore
Journal of Network and Computer Applications, 2005
Presented by Nam, Kwang Hyun
Intelligent Database Systems Lab
School of Computer Science & Engineering
Seoul National University, Seoul, Korea
Center for E-Business Technology
Seoul National University
Seoul, Korea
Contents
 Introduction
 Context modeling and reasoning
 The SOCAM architecture
 Performance evaluation
 Conclusion
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Introduction
 Context-aware service

A network service which uses various contexts and adapts itself
to the change of environment dynamically and automatically
 Architecture requirements

A common context model that can be shared by all devices and s
ervices

A set of services that perform
–
Context acquisition
–
Context discovery
–
Context interpretation
–
Context dissemination
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Proposal
 Model

An ontology-based context model using OWL
 System

A Service-Oriented Context-Aware Middleware (SOCAM)
–
Includes a set of independent services.
–
Supports

Acquiring various contexts from different context providers

Interpreting contexts through context reasoning

Delivering contexts in both push and pull modes.
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Context Model

Ontology


a vocabulary for representing knowledge about a domain and for des
cribing specific situations in a domain
An ontology-based approach

Allows to describe contexts semantically in a way which is independe
nt of programming language, underlying operating system or middle
ware

Context reasoning using first-order logic, temporal logic, and othe
rs enables to be done

Contexts are represented as first-order predicate calculus

Predicate(subject, value)
–
Location(John, bathroom)
–
Temperature(kitchen, 120)
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Context Ontology
 Two-layer hierarchical approach for designing context ontologi
es.

Common upper ontology
–

For the general concepts
Domain-specific ontologies
–
Apply to different sub-domains
의코
인논
 Benefit of two-layer hierarchical approach

Reduces the scale of context knowledge

Releases the burden of context processing for pervasive devices i
n each domain
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Upper(Generalized) Ontology
 Basic concepts

Person

Location

Computational
entity & activity
 Composition
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
14 classes

6 properties
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Domain-Specific ontology
 Domain-specific ontol
ogy defines

The details of gener
al concepts

Their properties
Example
IndoorSpace
subClassOf
Room
Entry
Corridor
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Context classification
 Direct context

Directly acquired or obtained from a context provider

Sensed context
–

Acquired from physical sensors (e.g. door’s status)
Defined context
–
Defined by a user (e.g. user’s foodPreference)
 Indirect context

Derived by interpreting direct context through context reasoning

Example
–
Showing can be inferred from Bathroom, (Water heater) On, (Door) Cl
osed
 Provide an additional property elements – owl:classifiedAs
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Class dependency
 Dependency

Captures the existence of a reliance of property associated with o
ne entity on another.

Provide an additional property elements – rdfs:dependsOn
 The importance of context dependency

Enable to incorporate probability and Bayesian networks to reaso
n about uncertain contexts.
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The SOCAM architecture
 A distributed middleware that transfers and converts various p
hysical spaces from which contexts are acquired into a semanti
c space where contexts can be easily shared and accessed by c
ontext-aware services
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The SOCAM architecture’s components


Context provider

Abstract useful contexts from heterogeneous sources

Convert them to OWL representation to share and reuse contexts

External (from external source) and Internal (from ubiquitous sensors)
Context interpreter

Provides logic reasoning services to process context information

Context reasoner

–
Provide deduced contexts
–
Detect inconsistency and conflict in context KB
Context KB
–
Provide a set of API’s for other service components to query, add, delete
or modify context knowledge
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The SOCAM architecture’s components
 Context database

Stores context ontologies and past contexts for a sub-domain
 Service locating service

Provides a mechanism where context providers and context inter
preter can advertise their presence
 Context-aware services

Make use of different level of contexts

Adapt the way they behave according to the current context
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Implementation
 SOCAM middleware implemented in J2SE 1.3.1
 Context interpreter implemented using Jena2-HP’s Semantic W
eb Toolkit
 Domain Specific ontologies implemented in OWL
 Home domain ontology

89 classes

156 properties
 Vehicle domain ontology

32 classes

57 properties
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Performance Evaluation (1/4)
Overhead of the two-layer ontology design
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Performance Evaluation (2/4)
The reasoning performance
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Performance Evaluation (3/4)
Reasoning comparison
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Performance Evaluation (4/4)
Average time for concurrent requests
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Conclusion
 Present a formal context model based on OWL
 The SOCAM middleware has been designed to support the bui
lding of context-aware services
 The evaluation results demonstrate a reasonable performance
 It is able to meet the requirements of context-aware systems
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Discussion
 Pros

Considering context dependency is novel.

Independent service components enables this architecture to ope
rate in distributed and heterogeneous networks.
 Cons

Performance is really reasonable?
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