A Platform for Rapid Composition of

Web Services in a Peer-to-Peer Environment

Quan Z. Sheng, Boualem Benatallah, Eileen Oi-Yan Mak

University of New South Wales, Sydney, Australia

Marlon DumasQueensland University of Technology, Brisbane, Australia

SELF-SERV provides a platform for rapid composition of Web se-rvices, where Web services are declaratively composed, and the resulting composite services are executed in a peer-to-peer and dynamic environment.

SELF-SERV distinguishes three types of services: elementary ser-vices, composite services, and service communities. Composite services are described through statecharts. Service communit-ies perform dynamic provider selection through selection poli-cies.

Pool of servicesand containers

User Layer

Communication Layer

is registered with

Elementaryservices

Containers

Composite services

is composed of

workflow database web-accessible programs

C1 C2 C3

CS1 CS2

ES1 ES2 ES4

Directory Layer

Conversation Layer

Service Layer

Internet

SOAP messages

Service registries

Service templates

1. Overview

SELF-SERV Service Manager

2. Service CreationThe Service Builder provides a statechart editor for describing composite service operations. It also offers search and browse facilities to locate operations from existing services and import them into composite services. It provides an editor for describing service operations, loading and configuring SELF-SERV built-in classes (e.g., linking an operation to a scoring service of a commun-ity).

Domestic Flight Booking (DFB)

Intl Travel Arrangement (ITA)

Accommodation Booking (AB)

Car Rental (CR)

AttractionsSearch (AS)

[domestic(destination)]

[not domestic(destination)]

[near(major_attraction, accommodation)]

[not near(major_attraction, accommodation)]

Complete Travel Service (CTS)

Intl. FlightBooking (IFB)

Travel Insurance (TI)

Intl Travel Arrangements Service (ITAS)

AS

DFB

ITA

AB

CR

IFB TI

CTS

wrapper

coordinator

3. Service DeploymentThe deployment of a composite service requires the generation and deployment of routing tables (i.e., precondition/postprocessing tables of each state of a composite service statechart). The routing tables (XML documents) are then uploaded into the hosts of the corresponding component services, together with the wrapper and coordinator classes.

4. Service Discovery EngineServices are published in a UDDI registry and located through the Service Discovery Engine.

5. Service Execution

CTS

ASS CRS ABS ITAS

TIS

IFBS

AS CR AB ITA TI

IFBASS

CF

IC

CF CF

IC IC IC

IC

IC

CFCF

CF CF

CFCF

IC

IC

wrapper

coordinator

control-flow notificationCF

service invocation/ completion

SELF-SERV adopts an orchestration model based on peer-to-peer interactions between software components hosted by the providers participating in the composition. The or-chestration of a com-position service exe-cution involves two types of messages: control flow notifica-tions and service invo-cations/completions.

CF

6. Performance Evaluation

No. of component service

Deployment cost (second)

15 20 30 40 50

8.9 10.1 13.1 15.9 19.0

No. of component service

Deployment cost (second)

60 70 80 90 100

21.8 25.9 30.2 32.9 34.1

Deployment cost of composite services.

We conducted several experiments to study the performance of SELF-SERV using a cluster of PCs.

The results show that the deployment speed is acceptable, and that the peer-to-peer approachto composite service execution leads to increa-sed throughput through better workload distri-bution.

Workload allocation.

Execution time with different message sizes.