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COCOA : Conversation-Based Service Composition for

Pervasive Computing Environments

Sonia Ben Mokhtar, Nikolaos Georgantas and Valérie Issarny

ICPS'06 : IEEE International Conference on Pervasive Services 2006

26-29 June 2006, Lyon, France

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Outline

• Background

• COCOA : COnversation based service COmposition for pervAsive computing environments

• Prototype Implementation and Evaluation

• Conclusion and Future Work

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Pervasive Computing Environments and SOA

e-shopping

Multimedia streaming

Travel reservation

Heterogeneity

e-learning

Standard Service description

Standard protocol

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Example Scenario

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Pervasive Computing Environments

• Mobile nodes host services providing various functionalities

• Mobile users need to perform tasks anytime anywhere, using functionalities of the pervasive environment

Challenges– Allow users to perform tasks, by composing “on the

fly” available networked services– Enable autonomy and adaptation to the

environment’s changes

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Issues & Requirements

Existing approaches to “ad hoc” service composition in pervasive computing environments

• Commonly assume that services have been pre-developed to integrate

• Poorly deal with the environment’s dynamics and heterogeneity

Requirements• Deal with the environment’s heterogeneity

Semantic Web services• Deal with the environment’s dynamics

Automating service discovery and composition

User tasks realized through dynamic composition of networked services

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Semantic Web services

Web Services • A software component developed using any language, deployed on

any platform, described using WSDL, accessible via remote calls using SOAP on top of internet protocols

• Web Services in pervasive computing environments (e.g. WSAmI [ISTS04])

Semantic Web Services

• Semantically annotating Web services descriptions using Ontologies

– Semantic annotation on top of WSDL, e.g., WSDL-S– Web Service Ontologies, e.g., OWL-S, WSMO,FLOWS, ROWS

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OWL-S based Model for Services and Tasks

Service• Workflow of high level provided capabilities• A set of non-functional properties

Task• Workflow of high level required capabilities

(abstract capabilities)• A set of non-functional requirements

Matching• High level capabilities (Service discovery

and selection)• Workflows (Service integration)

Browse

Browse

Browse

User Task

Networked Services

RequiredCapability

ProvidedCapabilities

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Abstract user task conversation

Service Discovery & Composition-COCOA

Service Composition

?: Service Discovery

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COCOA-SD: Semantic Matching of Service Capabilities

• Service Advertised capability (Adv)

• required inputs (Adv.In)

• provided outputs (Adv.Out)

• provided properties (Adv.P)

• Service Requested capability (Req)

• provided inputs (Req.In),

• required outputs (Req.Out)

• required properties (Req.P)

Client Service

Ontologies

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COCOA-CI: Modelling conversations as finite state automata

• A model to map OWL-S conversations to finite state automata

• A mapping rule for each OWL-S control construct (e.g. Choice, Sequence, While, Split)

• Translate the problem of dynamic conversation integration to an automata analysis problem

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COCOA-CI : Conversation Integration-Example

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COCOA-CI: Binding to Concrete Services

• Each composed capability corresponds to either an atomic or a composite process of a networked service

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Properties of COCOA-CI

• Workflow integration

• Interleaving

• The number of services to be composed is dynamic

• The degree of involvement of each composed service is dynamic

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COCOA-CI

2 3 4

1 3 2 41 2 3 4COCOA-CI

COCOA-CICOCOA-CI

Networked services

Networked services

Networked services-Env 2Networked services-Env 1

Service 1

Service 1 Service 2

Service 2

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COCOA in action…

COCOA-SD

COCOA-SD

COCOA-CI

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Prototype Implementation and Evaluation

Implementation of COCOA-CI

Runtime environment Java, Linux platform running on an Intel Pentium 4, 2.80 GHz CPU with 512 MB of memory

Services : from 1 to 100 of semantically equivalent capabilities

Evaluation of the runtime overhead produced by integrating conversations

Comparison with the XML parsing time of services and tasks (mandatory)

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Prototype Implementation and Evaluation

Task : composed of a single required capability The runtime overhead of COCOA-CI is negligible compared to the XML parsing time of services and task descriptions

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Prototype Implementation and Evaluation (2)

•Task : from 1 to 20 of semantically equivalent capabilities in sequence

The runtime overhead of COCOA-CI depends on the number intermediate paths assessed during the composition

Here : for a task composed of i capabilities there are 100 i

possible composition schemes

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Prototype Implementation and Evaluation (3)

• Realistic scenario• 20 required capabilities

• 30 available capabilities

• Various control constructs32 ms for finding the 2 possible compositions among 36 intermediate

compositions 152 ms for XML parsing of service and task descriptions

In most realistic cases the runtime overhead of COCOA-CI is negligible compared to XML parsing time

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Conclusion & Future work

COCOA : Conversation-based Service Composition in Pervasive Computing Environments

• A flexible approach for dynamically composing services to perform a user task

• Built upon Web services and Semantic Web paradigms

• Based on conversation integration

Ongoing work • Advanced prototype implementation (including QoS- and Context-

awareness) underway as a part of the European IST AMIGO project

• Integration of COCOA into a semi-distributed discovery protocol adapted for pervasive computing environments [Sailhan,Percom’05]

• Efficient matching of semantic Web service capabilities

• Reconfiguration of the composed user task at runtime

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Questions ?

Allez Les Bleus !