university of jyvÄskylÄ service portability framework for integrated communication environments...

UNIVERSITY OF JYVÄSKYLÄ

Service Portability Framework for Integrated Communication

EnvironmentsDmytro Zhovtobryukh

University of Jyväskylä

Veikko HaraTeliaSonera Corporation

IASW-2005 ConferenceAugust 27, 2005

27.08.2005 University of Jyväskylä, IASW 2005

2

Research Overview

MSc degree in Mobile Computing from the University of Jyväskylä, 2002Currently making research on a PhD thesisThe research is carried out in collaboration with TeliaSonera corporation and is motivated by their needsResearch interests:

Network InteroperabilityPervasive ComputingContext AwarenessAdaptive Applications


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Contents

Motivation

Service Portability Framework

Service adaptation mechanisms

Applicability to Semantic Web environments

Conclusions


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Evolution of Distributed Computing

Portable computing is an interim step between mobile and pervasive computing

DistributedComputing

remote communicatio

nsremote information

accessdistributed security

replication

fault tolerance

Mobile Computin

gmobile

networking

mobile information

accesslocation awareness

power management

Pervasive Computin

gsmart spaces

ubiquitous information

accessinvisibility

proactivity

Portable Computin

gnetwork

interoperability

context awarenessadaptive

applications

teleporting


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Challenges

Service-level support for cross-network mobility

services

usersapplications

environments

provided in the form

consumed by

operate in roam between

Infra-structure support

Service independence of environments

Dynamic service adaptation for quality and continuity preservation

Solution: Context Aware Infrastructure Support for Service Portability


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Service Portability

Service portability is a capability of a service to be consumed:

through diverse environmentsby various usersusing different devices

A variety of implementations for the same serviceAdaptive provisioning of a service through dynamically changing environments


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Goals

Seamless provision of any service through any type of environment

decoupling services and service applications

maintenance of the global unique service instance

on-demand construction of service applications as specific service implementations

adaptation of service applications instead of services

continuous service sessions


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Two-phase Service Provisioning

Allows decoupling of services and service applicationsComprises two distinct phases:

service creation: design of a generic serviceservice delivery: service application construction and run-time adaptation

Service provisioning architecture relies upon a context aware reflective middleware infrastructure


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Service Portability Framework

Environment changes not only on a handover to a different network system, but also, for example, on a user’s switchover to a different terminal

Generic Service

Ap

plic

atio

n 1

Ap

plic

atio

n 2

*

Ap

plic

atio

n 2

devices

protocols

resources

media

Environment 1 Environment 2 Environment 3

bu

ild

bu

ild

service context

adapt

Context-Aware Middleware

acquire contexts

update contextsacquire

contexts

Generic service is designed wrt. the actual serviceEnvironment includes computing environment, physical surroundings, user’s terminal equipmentApplications are ported between environments instead of services


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Service Creation

Generic Service:consists of the service core functionality and its description (metadata)is relieved of any specific implementation detailsunique, global and unambiguous

Benefits:the service is easily recognizabledoes not shrink the range of possible implementationsenables service porting between environmentspotentially simplifies service composition


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Service Delivery

Reflects an application’s lifecycleTwo subphases:

load-time, i.e. build-timerun-time

Load-time:Application is constructed from generic service wrt. initial environmental conditions (initial context)

Run-time:Application adapts or gets adapted whenever essential contextual changes occurIdeally, such run-time adaptation leads to preservation of service session continuity


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Vertical Services vs. Horizontal Services (I)

Vertical servicesprovided to an end userhave rigid implicit structurecannot dynamically adapt

Horizontal servicesprovided by a system to other services and processesperform highly specialized system functions (e.g. network transport, traffic management, etc.)are local for every other environmentreflect system layering


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Vertical Services vs. Horizontal Services (II)

Transition from Vertical to Horizontal servicesallows for a flexible structure of a vertical service

variable system functionality within a vertical service

adjustment of system functionality of vertical service to changing horizontal services

necessity of a specific application design framework supporting reconfigurability


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Application Design Framework

Modular structureaccurate vertical layering of system functionalityclassification of system functionality into primitive functions on each horizontal layerservice primitives, i.e. modules, being pieces of executable program codeunified interface between modules

Reconfigurabilityprimitives can be added, removed or substituted at run-timeprimitives are provided by the horizontal services running in the environment


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Application Construction

creating generic service

C1 C2 … Cc

Content layer

M1 M2 … Mm

Generic Service

A1 A2 … Aa

Application layer

S1 S2 … Ss

System layer

T1 T2 … Tt

Transport layer

Network layerN1 N2 … Nn

Service

Service Primitives

Network

Transport

System

Horizontal Services

Vertical Service

Application

Middleware

launch

Service Creation

Service Delivery

Environment

service metadata

locating horizontal services

extracting service primitives

analysing initial conditions

building application

allocating service primitives

assembling vertical service

finalizing application

launching application


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Context-based AdaptationAll adaptation-related data are treated as contextContext definition (by A.Dey):

Context is any information that can be used to characterize the situation of an entity. An entity is a person, place, or object that is considered relevant to the interaction between a user and an application, including the user and applications themselves.

Network contextsphysical: location, signal strength, levels of interference, etc. – measured by sensorssystem: resource levels, links’ throughput, error rates, etc. – measured by monitors

Service context: metadata within the generic serviceUser context: user profilesDevice context: device profiles


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Service Adaptation Framework

Adaptation essence: reselection of service primitives constituting the applicationAdaptation procedure is basically under control of the context aware middleware infrastructure

P11 P12 P1k

P2lP21 P22

PnmPn2Pn1

…

…

…

…

Service Application

Context Reasoning Engine

CoI Board

Context Model

P11 P12 P1p

P2rP21 P22

PnsPn2Pn1

…

…

…

…

Service Primitives

System Contexts

Logical ContextsUpdate

Direct contexts

Notify Changes

Substitute

Substitute

Notify Changes

Register CoI

Analyze

- Context providers Pij – Service Primitives CoI –Context of Interest

Context Manager

Context Acquisition Proxy

Context Knowledge Base

Context Management Module

Track CoI

Direct contexts


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Context Aware MiddlewareContext Acquisition Proxy

acquires context data from context sourcesfilters inessential readingspossibly generalizes the data received

Context Managerdisseminates context data between entitiesmanages and updates context knowledge base

Context Reasoning Engineinfers high-level contextsperforms context reasoning and aggregationmakes adaptation decisions

Context Knowledge Basestores contextual information wrt. the context modelcomprises System Contexts and Context Model repositories


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Background Adaptation

Default type of adaptation

Is entirely handled by the middleware

The application may be even unaware of the adaptation performed on it

Inappropriate service primitives typically reside on the layers corresponding to horizontal services provided by a local environment

Preserves application’s operability and cross-network portability


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Application Aware Adaptation

Middleware cannot sensibly manage application-specific issuesUtilized if the middleware cannot resolve the problem by its own strength, or the application explicitly requires the adaptationManaged by the application alone or with assistance of the middlewareInappropriate service primitives belong to the layers that are not transparent to the application, i.e. concern the service, not the environmentThe application can register certain ”contexts of interest” and adapt wrt. themPreserves service quality and achieves application-specific goals


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User Aware Adaptation

Neither the middleware, nor the application can solve the problem by their own strengthAdaptation decision is made consciously by the userFeatures a so-called ”corrective action”, a solution proposed by the application and the middleware to the userMinimal distraction to the user is quite a challengePreserves service quality and user preferences


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Why Semantic Web?

Web Service Architecture (WSA) provides support for two-phase service provisioningService portability framework resembles WSA with certain amendments, which can be realized within the middleware architecture without altering WSAOntologies are currently the most suitable tool for modeling contextSemantic Web services are already provided with metadataPractically, the infrastructure for service portability is easier to implement within a single enterprise network rather than on a wide scale of public communication systems


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Ontologies for Modeling Context

High flexibility and manageabilityPossibility for distributed compositionCapturing incomplete and ambiguous informationHigh level of formalityApplicability to existing environmentsProvide means for contextual reasoning (in particular in OWL format)In real enterprise environments context sources may already provide information in an ontological form


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A Scenario for SW Environment

Web service corresponds to the notion of Generic ServiceSemantic service description is the source of the service contextThe environment is comprehensively described within the enterprise ontology

Context Reasoning Engine

Context Manager

Context Model

Context Acquisition Proxy

Application

Service Provider Service Requestor

WS

EO

SP

low-level contexts

invoke service

service description

high-level contexts

adapt

provide

EO – Enterprise OntologySP – Service PrimitivesWS – Web Service


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Conclusions

Context awareness can play a vital role for building up network interoperability and increasing service reusability across diverse communication environmentsDecoupling service and applications simplifies service creation, alleviates efforts on run-time service adaptation and increases service scalabilityThe use of reflective middleware enables efficient run-time adaptation and hence portability of services is achievedBringing context to Web services along with semantics will make them ever more flexible and intelligent


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Future Work

The issues to be still addressed:Programming model for reconfigurable applications

Extraction of service primitives wrt. underlying system architecture

Distributed composition of the middleware architecture

Context modeling approach

Context dissemination protocols


27

Thank you

Questions?

university of jyvÄskylÄ service portability framework for integrated communication environments...

Documents

service creation

service portability

service adaptive provisioning

twophase service provisioning

global unique service

diverse environments

changing environments

decoupling of services