Introduction Prelims Agents Related Work Conclusion

Provider-Composer Negotiations forSemantic Robustness in Service

Compositions

Nikolay Mehandjiev Freddy Lécué Usman Wajid

Centre for Service ResearchThe University of Manchester

Booth Street East, Manchester, UK

ICSOC-ServiceWave,November 24-26, 2009

Stockholm, Sweden

Introduction Prelims Agents Related Work Conclusion

Outline

1 Introduction

2 Preliminaries

3 Agents and Template-based Composition

4 Related Work

5 Conclusion

Introduction Prelims Agents Related Work Conclusion

Scope

Introduction and Scope

Conventional and Web ServicesIntertwine

both areas can “learn” from each other;

e.g. produce better software byconsidering service providers.

Role of Service Providers in Web Service Composition

Currently only in service quality and contracts.

This is OK for small and cheap services,

but sub-optimal for complex and evolving assemblies.

This Talk:

demonstrates one particular benefit of considering service providers;

focuses on achieving robust composition in a large search space;

assumes template-based composition.

Introduction Prelims Agents Related Work Conclusion

Scope

Introduction and Scope

Conventional and Web ServicesIntertwine

both areas can “learn” from each other;

e.g. produce better software byconsidering service providers.

Role of Service Providers in Web Service Composition

Currently only in service quality and contracts.

This is OK for small and cheap services,

but sub-optimal for complex and evolving assemblies.

This Talk:

demonstrates one particular benefit of considering service providers;

focuses on achieving robust composition in a large search space;

assumes template-based composition.

Introduction Prelims Agents Related Work Conclusion

Scope

Introduction and Scope

Conventional and Web ServicesIntertwine

both areas can “learn” from each other;

e.g. produce better software byconsidering service providers.

Role of Service Providers in Web Service Composition

Currently only in service quality and contracts.

This is OK for small and cheap services,

but sub-optimal for complex and evolving assemblies.

This Talk:

demonstrates one particular benefit of considering service providers;

focuses on achieving robust composition in a large search space;

assumes template-based composition.

Introduction Prelims Agents Related Work Conclusion

Template-based Service Composition

Template-based Composition of Semantic Services

Service Composition:

aims to satisfy the need for a service by bringing together existing ones;

manual or automated;

“from scratch” or using existing templates.

Template Instantiation:

A template contains a set of tasks: unbound service specifications.

The aim is to find the optimal service to instantiate each task.

We focus on optimising the “data fit” between service inputs and precedingoutputs.

Functional Description

DescriptionAndName

ParametersInput Output

Parameters

Pre-Conditions Post−Conditions Functional View of Services:

Formally specified inputs and outputs.

Formally specified service aim.

Pre-conditions and post-conditions are semanticexpressions.

Introduction Prelims Agents Related Work Conclusion

Template-based Service Composition

Template-based Composition of Semantic Services

Service Composition:

aims to satisfy the need for a service by bringing together existing ones;

manual or automated;

“from scratch” or using existing templates.

Template Instantiation:

A template contains a set of tasks: unbound service specifications.

The aim is to find the optimal service to instantiate each task.

We focus on optimising the “data fit” between service inputs and precedingoutputs.

Functional Description

DescriptionAndName

ParametersInput Output

Parameters

Pre-Conditions Post−Conditions Functional View of Services:

Formally specified inputs and outputs.

Formally specified service aim.

Pre-conditions and post-conditions are semanticexpressions.

Introduction Prelims Agents Related Work Conclusion

Template-based Service Composition

Template-based Composition of Semantic Services

Service Composition:

aims to satisfy the need for a service by bringing together existing ones;

manual or automated;

“from scratch” or using existing templates.

Template Instantiation:

A template contains a set of tasks: unbound service specifications.

The aim is to find the optimal service to instantiate each task.

We focus on optimising the “data fit” between service inputs and precedingoutputs.

Functional Description

DescriptionAndName

ParametersInput Output

Parameters

Pre-Conditions Post−Conditions Functional View of Services:

Formally specified inputs and outputs.

Formally specified service aim.

Pre-conditions and post-conditions are semanticexpressions.

Introduction Prelims Agents Related Work Conclusion

Semantic Web Services

Semantic Web Services

Parameters (i.e., Input and Output) of Web services in semanticWeb are concepts referred to in an ontology T :

WSDL-S, SA-WSDL (W3C Proposed Recommendation);OWL-S profile level;WSMO capability level.

Introduction Prelims Agents Related Work Conclusion

Web Service Composition and its Semantic Links

Semantic Link: Semantic connection between services;... more particulary between Output and Input parameters;... denoted by sly,x and valued by SimT (Out_sy , In_sx);

SimT is reduced to the five matchmaking functions [M.Paolucciet al. ISWC’02, Li and Horrocks WWW’03]:

Exact i.e., T |= Out_sy ≡ In_sx ; XPlugIn i.e., T |= Out_sy v In_sx ; XSubsume i.e., T |= In_sx v Out_sy ; 7

Intersection i.e., T 6|= Out_sy u In_sx v ⊥; 7

Disjoint i.e., T |= Out_sy u In_sx v ⊥; X

For 7 we need some refinements: Extra Description.

Web service: sxSemantic connection:

S Input Parameters

y

S Input Parameters

xS Output Parameters

y

S Output Parameters

x

Web service: sy

SimT

Out_sy In_sx

Introduction Prelims Agents Related Work Conclusion

Web Service Composition and its Semantic Links

Semantic Link: Semantic connection between services;... more particulary between Output and Input parameters;... denoted by sly,x and valued by SimT (Out_sy , In_sx);

SimT is reduced to the five matchmaking functions [M.Paolucciet al. ISWC’02, Li and Horrocks WWW’03]:

Exact i.e., T |= Out_sy ≡ In_sx ; XPlugIn i.e., T |= Out_sy v In_sx ; XSubsume i.e., T |= In_sx v Out_sy ; 7

Intersection i.e., T 6|= Out_sy u In_sx v ⊥; 7

Disjoint i.e., T |= Out_sy u In_sx v ⊥; X

For 7 we need some refinements: Extra Description.

Web service: sxSemantic connection:

S Input Parameters

y

S Input Parameters

xS Output Parameters

y

S Output Parameters

x

Web service: sy

SimT

SlowNetWorkConnectionNetWorkConnection

Introduction Prelims Agents Related Work Conclusion

Robustness

Non Robust Semantic Links in Web Service Composition

The open issue: How transform a non robust semantic linkSimT (Out_sy , In_sx) in its robust form?

The suggested approach: by retrieving the Extra Description H- information contained by In_sx and not by Out_sy throughConcept Abduction or Concept Difference.

T. Di Noia, E. Di Sciascio et al.Abductive matchmaking using description logics.In IJCAI, pages 337–342, Acapulco, Mexico, 2003. MK.

G. Teege.Making the difference: A subtraction operation for DLs.In KR, pages 540–550, San Francisco, California, 1994.

Introduction Prelims Agents Related Work Conclusion

Robustness

Non Robust Semantic Links in Web Service Composition

The open issue: How transform a non robust semantic linkSimT (Out_sy , In_sx) in its robust form?

The suggested approach: by retrieving the Extra Description H- information contained by In_sx and not by Out_sy throughConcept Abduction or Concept Difference.

T. Di Noia, E. Di Sciascio et al.Abductive matchmaking using description logics.In IJCAI, pages 337–342, Acapulco, Mexico, 2003. MK.

G. Teege.Making the difference: A subtraction operation for DLs.In KR, pages 540–550, San Francisco, California, 1994.

Introduction Prelims Agents Related Work Conclusion

Robustness

Concept Abduction in Web Service Composition

Definition (Concept Abduction)

Let L be a DL, Out_sy , In_sx be two concepts in L, and T be a set ofaxioms in L. A Concept Abduction Problem (CAP), denoted as〈L, Out_sy , In_sx , T 〉 is finding a concept H ∈ L such thatT |= Out_sy u H v In_sx .

The Extra Description H represents what is underspecified in Out_syin order to completely satisfy In_sx ;⇒ Explains why Out_sy and In_sx can not be chained by a robust

semantic link.

The Common Description Out_sy u In_sx refers to informationrequired by In_sx and effectively provided by Out_sy .

Introduction Prelims Agents Related Work Conclusion

Robustness

Concept Abduction with an Example

Definition (Concept Abduction)

Let L be a DL, Out_sy , In_sx be two concepts in L, and T be a set ofaxioms in L. A Concept Abduction Problem (CAP), denoted as〈L, Out_sy , In_sx , T 〉 is finding a concept H ∈ L such thatT |= Out_sy u H v In_sx .

e.g., in case of non robust semantic link valued by the Subsumematch level.

Web service: sx

S Input Parameters

x

S Output Parameters

x

S Output Parameters

Web service: sy

S Input Parameters

y

y

Introduction Prelims Agents Related Work Conclusion

Robustness

Concept Abduction with an Example

Definition (Concept Abduction)

Let L be a DL, Out_sy , In_sx be two concepts in L, and T be a set ofaxioms in L. A Concept Abduction Problem (CAP), denoted as〈L, Out_sy , In_sx , T 〉 is finding a concept H ∈ L such thatT |= Out_sy u H v In_sx .

e.g., in case of non robust semantic link valued by the Subsumematch level.

Web service: sx

S Input Parameters

x

S Output Parameters

x

S Output Parameters

Web service: sy

S Input Parameters

y

y

Introduction Prelims Agents Related Work Conclusion

Robustness

Concept Abduction in Web Service Composition

Definition (Concept Abduction)

Let L be a DL, Out_sy , In_sx be two concepts in L, and T be a set ofaxioms in L. A Concept Abduction Problem (CAP), denoted as〈L, Out_sy , In_sx , T 〉 is finding a concept H ∈ L such thatT |= Out_sy u H v In_sx .

Explains Why a semantic link is not robust...... hence provides a way to replace (How) a non robust semanticlink in its robust form:

Subsume match level 7⇒ Exact match level X;Intersection match level 7⇒ PlugIn match level X.

Introduction Prelims Agents Related Work Conclusion

Agents and Template-based Composition

Service Providers and the Service Composer are agents

The Service Composer selects a Composition Template andadvertises it on a noticeboardService Providers watch the noticeboards of interest and bid toprovide services

Semantic Composition Template

is a graph containing a set of tasks Ti as its nodes and a set ofAbstract Semantic Links slAi,j as its edges.

Introduction Prelims Agents Related Work Conclusion

Service Providers Bidding to Instantiate Tasks

Service Providers Bidding to Instantiate Tasks

Service Providers are represented by Software Agents

Agents monitor noticeboards for suitable tasks for their services.A service s is considered suitable for task T if:

1 The service s achieves the same goal as T .2 The pre-conditions of s are implied by the pre–conditions of T .3 The post-conditions of s imply the post-conditions of T .4 SimT (In_T , In_s) is PlugIn.5 SimT (Out_s, Out_T ) is PlugIn.

Introduction Prelims Agents Related Work Conclusion

Protocol Outline

Protocol Outline

For each non-robust abstract link slAi,jthe service composer agent calculates its HTi ,Tj ;and initiates a three-phase negotation protocol, involving theproviders of services si and sj ,aiming to select services which provide robust instantiation of thesemantic link.

The assumptions behind three phases are:1 Phase 1: robust composition “for free” (i.e. w/out extra services),

using differences in specs between a task and its services;2 Phase 2: additional services (and usage fees), but no

modifications;3 Phase 3: service providers adapt services against payment.

Introduction Prelims Agents Related Work Conclusion

Protocol Outline

Protocol Outline

For each non-robust abstract link slAi,jthe service composer agent calculates its HTi ,Tj ;and initiates a three-phase negotation protocol, involving theproviders of services si and sj ,aiming to select services which provide robust instantiation of thesemantic link.

The assumptions behind three phases are:1 Phase 1: robust composition “for free” (i.e. w/out extra services),

using differences in specs between a task and its services;2 Phase 2: additional services (and usage fees), but no

modifications;3 Phase 3: service providers adapt services against payment.

Introduction Prelims Agents Related Work Conclusion

Protocol Detail - Phase 1

Protocol Detail - Phase 1

Step 1

1 Service Composer sends CFP(HTi ,Tj ) to all providers of si ;

2 The response depends on Out_si compared to HTi ,Tj :

a) Proposal: if T |= Out_si v HTi ,Tj u Out_Ti .b) Refuse: If T |= Out_si u HTi ,Tj v ⊥.c) Counter-Proposal:If there is satisfiable intersection, i.e.,

T 6|= Out_si u HTi ,Tj v ⊥, the provider will propose Out_si

instead.

Step 2

1 Service Composer sends CFP({Out_si}) to providers of sj .

2 The responses depend if In_sj subsumes any of the

counter-proposals:a) Proposal: if SimT (Out_si , In_sj ) is of a PlugIn type;b) Counter-Proposal: If SimT (Out_si , In_sj ) is an

Intersection type, the counter-proposal is the extradescription required for this concrete semantic link sli,j i.e.,T |= Out_si u Hsi ,sj v In_sj . We have “Paired Offer”.

If the second step ends up with counter-proposals rather thanproposals, the composer will initiate the second phase of negotiation.

Introduction Prelims Agents Related Work Conclusion

Protocol Detail - Phase 1

Protocol Detail - Phase 1

Step 1

1 Service Composer sends CFP(HTi ,Tj ) to all providers of si ;

2 The response depends on Out_si compared to HTi ,Tj :

a) Proposal: if T |= Out_si v HTi ,Tj u Out_Ti .b) Refuse: If T |= Out_si u HTi ,Tj v ⊥.c) Counter-Proposal:If there is satisfiable intersection, i.e.,

T 6|= Out_si u HTi ,Tj v ⊥, the provider will propose Out_si

instead.

Step 2

1 Service Composer sends CFP({Out_si}) to providers of sj .

2 The responses depend if In_sj subsumes any of the

counter-proposals:a) Proposal: if SimT (Out_si , In_sj ) is of a PlugIn type;b) Counter-Proposal: If SimT (Out_si , In_sj ) is an

Intersection type, the counter-proposal is the extradescription required for this concrete semantic link sli,j i.e.,T |= Out_si u Hsi ,sj v In_sj . We have “Paired Offer”.

If the second step ends up with counter-proposals rather thanproposals, the composer will initiate the second phase of negotiation.

Introduction Prelims Agents Related Work Conclusion

Protocol Detail - Phases 2 and 3

Protocol Detail - Phases 2 an 3

Step 1

1 Service Composer sends CFP(MatrixH) to all providers of si ;2 MatrixH contains all Paired Offers, padded with HTi ,Tj ;

3 The response can be one of the following:a) Statement-of-Interest: “Buying Time” to find partners.b) Proposal: When ready to provide the missing information.c) Failure: If the service provider cannot help.

Step 2

1 Service Composer sends CFP({Out_si}) to providers of sj .

2 The response options are the same as for Step 1.3 For Phase 2, both si and sj consider forming partnerships and

coalitions;4 For Phase 3, both sets consider adapting their own service

offerings.

If more than one positive response is received, the general serviceselection criteria are used.

Introduction Prelims Agents Related Work Conclusion

Protocol Detail - Phases 2 and 3

Protocol Detail - Phases 2 an 3

Step 1

1 Service Composer sends CFP(MatrixH) to all providers of si ;2 MatrixH contains all Paired Offers, padded with HTi ,Tj ;

3 The response can be one of the following:a) Statement-of-Interest: “Buying Time” to find partners.b) Proposal: When ready to provide the missing information.c) Failure: If the service provider cannot help.

Step 2

1 Service Composer sends CFP({Out_si}) to providers of sj .

2 The response options are the same as for Step 1.3 For Phase 2, both si and sj consider forming partnerships and

coalitions;4 For Phase 3, both sets consider adapting their own service

offerings.

If more than one positive response is received, the general serviceselection criteria are used.

Introduction Prelims Agents Related Work Conclusion

Service Composition

Related Work - Robustness in Service Composition

At Functional LevelMost of FLC consider not robust semantic links hence someinconsistencies in the composition model:

e.g. [O.Lassila and S.Dixit AAAI’04] and [Zhang et al. ICWS’03]with Exact, Subsume, PlugIn and Disjoint;e.g. [J.Cardoso and A.Sheth JIIS’03] with computation of syntacticsimilarity;e.g. [T.Di Noia et al. WWW’05];

In the same direction ...Semi-Automation of Robust Composition (End-User Assistance)[F.Lécué et al. ICWS’07];Authors of [F.Lécué and A.Delteil AAAI’07] suggest to use theConcept Difference (more costly) [Teege KR’94] and not theConcept Abduction.

Introduction Prelims Agents Related Work Conclusion

Service Composition

Related Work - Robustness in Service Composition

At Functional LevelMost of FLC consider not robust semantic links hence someinconsistencies in the composition model:

e.g. [O.Lassila and S.Dixit AAAI’04] and [Zhang et al. ICWS’03]with Exact, Subsume, PlugIn and Disjoint;e.g. [J.Cardoso and A.Sheth JIIS’03] with computation of syntacticsimilarity;e.g. [T.Di Noia et al. WWW’05];

In the same direction ...Semi-Automation of Robust Composition (End-User Assistance)[F.Lécué et al. ICWS’07];Authors of [F.Lécué and A.Delteil AAAI’07] suggest to use theConcept Difference (more costly) [Teege KR’94] and not theConcept Abduction.

Introduction Prelims Agents Related Work Conclusion

Agent Negotiation and Coalition Formation

Related Work - Agent Negotiation

Using Agents for Web Service Composition

Mostly focused on contracts and norms, e.g. [Kollingbaum et.al.at WISER’2006];Only a few focus on the composition problem, e.g. [Hassine et.al.at ISWC’06];Agents for robust composition of WS instances are used in[Lécué et.al. at ECOWS’09].

Using Agents to Represent Service Providers and Requesters

Mature work on negotiation and coalition formation protocols;“Service” is a core concept in agent research but not directlylinked to Semantic Web Services;There are some examples of work on agents collaborating toprocure web services [Abdoessalam et.al. WETICE’04]

Introduction Prelims Agents Related Work Conclusion

Agent Negotiation and Coalition Formation

Related Work - Agent Negotiation

Using Agents for Web Service Composition

Mostly focused on contracts and norms, e.g. [Kollingbaum et.al.at WISER’2006];Only a few focus on the composition problem, e.g. [Hassine et.al.at ISWC’06];Agents for robust composition of WS instances are used in[Lécué et.al. at ECOWS’09].

Using Agents to Represent Service Providers and Requesters

Mature work on negotiation and coalition formation protocols;“Service” is a core concept in agent research but not directlylinked to Semantic Web Services;There are some examples of work on agents collaborating toprocure web services [Abdoessalam et.al. WETICE’04]

Introduction Prelims Agents Related Work Conclusion

Conclusion and Future Work

ConclusionTemplate-based Service composition as a composition ofSemantic links;Considering service providers represented as agents can helpby:

robustness of semantic links;phased protocol to minimise robustness costs;near-linear complexity using Extra Descriptions.

Further work in the areaLinking instance-based and template-based compositions;Optimising across different semantic links - coalition formation;Optimising in case of “split” and “join” semantic links.

Introduction Prelims Agents Related Work Conclusion

Conclusion and Future Work

ConclusionTemplate-based Service composition as a composition ofSemantic links;Considering service providers represented as agents can helpby:

robustness of semantic links;phased protocol to minimise robustness costs;near-linear complexity using Extra Descriptions.

Further work in the areaLinking instance-based and template-based compositions;Optimising across different semantic links - coalition formation;Optimising in case of “split” and “join” semantic links.

Introduction Prelims Agents Related Work Conclusion

Questions?