A service-oriented middleware for building context-aware services Center for E-Business Technology Seoul National University Seoul, Korea Tao Gu, Hung.

A service-oriented middleware for building context-aware services

Center for E-Business TechnologySeoul National University

Seoul, Korea

Tao Gu, Hung Keng Pung, Da Qing ZhangInstitute for Infocomm Research, SingaporeJournal of Network and Computer Applications, 2005 Presented by Nam, Kwang HyunIntelligent Database Systems LabSchool of Computer Science & EngineeringSeoul National University, Seoul, Korea

Copyright 2008 by CEBT

Contents

Introduction

Context modeling and reasoning

The SOCAM architecture

Performance evaluation

Conclusion

2


Introduction

Context-aware service

A network service which uses various contexts and adapts itself to the change of environment dynamically and auto-matically

Architecture requirements

A common context model that can be shared by all devices and services

A set of services that perform

– Context acquisition

– Context discovery

– Context interpretation

– Context dissemination

3


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.

4


Context Model

Ontology

a vocabulary for representing knowledge about a domain and for describing specific situations in a domain

An ontology-based approach

Allows to describe contexts semantically in a way which is in-dependent of programming language, underlying operating system or middleware

Context reasoning using first-order logic, temporal logic, and others enables to be done

Contexts are represented as first-order predicate calculus

Predicate(subject, value)

– Location(John, bathroom)

– Temperature(kitchen, 120)

5


Context Ontology

Two-layer hierarchical approach for designing context on-tologies.

Common upper ontology

– For the general concepts

Domain-specific ontologies

– Apply to different sub-domains

Benefit of two-layer hierarchical approach

Reduces the scale of context knowledge

Releases the burden of context processing for pervasive devices in each domain

6

의코인논


Upper(Generalized) Ontology

7

Basic concepts Person

Location

Computa-tional entity & activity

Composition 14 classes

6 properties


Domain-Specific ontology Domain-specific on-

tology defines

The details of general concepts

Their properties

8

Example

subClassOf

IndoorSpace

Room

Corridor

Entry


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 reason-ing

Example

– Showing can be inferred from Bathroom, (Water heater) On, (Door) Closed

Provide an additional property elements – owl:classifiedAs

9


Class dependency

Dependency

Captures the existence of a reliance of property associated with one entity on another.

Provide an additional property elements – rdfs:dependsOn

The importance of context dependency

Enable to incorporate probability and Bayesian networks to reason about uncertain contexts.

10


The SOCAM architecture

A distributed middleware that transfers and converts var-ious physical spaces from which contexts are acquired into a semantic space where contexts can be easily shared and accessed by context-aware services

11


The SOCAM architecture’s com-ponents

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

12


The SOCAM architecture’s com-ponents

Context database

Stores context ontologies and past contexts for a sub-do-main

Service locating service

Provides a mechanism where context providers and context interpreter can advertise their presence

Context-aware services

Make use of different level of contexts

Adapt the way they behave according to the current con-text

13


Implementation

SOCAM middleware implemented in J2SE 1.3.1

Context interpreter implemented using Jena2-HP’s Se-mantic Web Toolkit

Domain Specific ontologies implemented in OWL

Home domain ontology

89 classes

156 properties

Vehicle domain ontology

32 classes

57 properties

14


Performance Evaluation (1/4)

15

Overhead of the two-layer ontology design



16

The reasoning performance



17

Reasoning comparison



18

Average time for concurrent re-quests


Conclusion

Present a formal context model based on OWL

The SOCAM middleware has been designed to support the building of context-aware services

The evaluation results demonstrate a reasonable per-formance

It is able to meet the requirements of context-aware sys-tems

19


Discussion

Pros

Considering context dependency is novel.

Independent service components enables this architecture to operate in distributed and heterogeneous networks.

Cons

Performance is really reasonable?

20

A service-oriented middleware for building context-aware services Center for E-Business Technology Seoul National University Seoul, Korea Tao Gu, Hung.

Documents

context ontologies

context reasoningexample

burden of context processing

contextaware systems

cebtuppergeneralized

common upper ontology

specific situations

serviceoriented middleware