Exercise: Web Service Composition 1

Basic of Web Service Composition using WS-BPEL

WS-BPEL（Web Service Business Process Execution Language）, standarlized by OASIS, is a language that define the inteaction of business process by multiple Web servicces．WS-BPEL can realize business process for Web service composition, based on Web service standards like SOAP and WSDL.

Process described by WS-BPEL（BPEL process） is defined as collection of Web services based on some decided sequences. The Web services used in the BPEL process is handled as a black box. BPEL process itself can be opened as Web service.

The purpose of this exercise is to learn and practice how to describe BPEL process for Web service composition by using WS-BPEL design tools (e.g., Eclipse BPEL Designer). In this exercise, you are required to realize the composite back translation service (translate the source from language A to language B and then traslate the result from language B back to language A) by connecting two atomic machine translation services provided by the Language Grid. The back translation is always used for evaluation of the machine translation quality.

Activity and Structure of BPEL Process

BPEL process is described in XML. We will show the XML structure example of back translation example as follows.

<?xml version="1.0" encoding="UTF-8"?>
<bpws:process name="Backtrans"
    targetNamespace="http://www.ai.soc.i.kyoto-u.ac.jp/process/Backtrans/"
    exitOnStandardFault="yes"
    suppressJoinFailure="yes"
    xmlns:bpws="http://docs.oasis-open.org/wsbpel/2.0/process/executable"
    xmlns:ns="http://www.ai.soc.i.kyoto-u.ac.jp/process/Backtrans/Artifacts"
    xmlns:ns0="http://langrid.ai.soc.i.kyoto-u.ac.jp/langrid-service_1_2/services/JServer" 
    xmlns:tns="http://www.ai.soc.i.kyoto-u.ac.jp/process/Backtrans/">

    <!?import definition-->
    <bpws:import importType="http://schemas.xmlsoap.org/wsdl/"
        location="../wsdl/Backtrans.wsdl" 
        namespace="http://www.ai.soc.i.kyoto-u.ac.jp/process/Backtrans"/>
    <bpws:import importType="http://schemas.xmlsoap.org/wsdl/"
        location="..." 
        namespace="..."/>

    <!?partner link definition-->
    <bpws:partnerLinks>
        <bpws:partnerLink name="TranslateAltPL"
            partnerLinkType="ns:TranslatePLT" 
            partnerRole="translator"/>
        <bpws:partnerLink name="..."
            partnerLinkType="..." 
            partnerRole="..."/>
    </bpws:partnerLinks>

    <!?variable definition-->
    <bpws:variables>
        <bpws:variable messageType="tns:translateRequest" 
            name="backtransRequest"/>
        <bpws:variable messageType="..." 
            name="..."/>
    </bpws:variables>

    <!--activity definition in the sequence structure-->
    <bpws:sequence>
        <bpws:receive.../>
        <bpws:assign...>...</bpws:assign>
        <bpws:invoke...>...</bpws:invoke>
        <bpws:assign...>...</bpws:assign>
        <bpws:reply.../>
    </bpws:sequence>
</bpws:process>

Tasks in BPEL process is described as activities. Different types of activities have different functions. Here we explain some activities that will be used in this exercise.

Steps for creating BPEL Process

Creation of BPEL process include following steps: process definition, process deployment, and test．

Practice of BPEL Process Creation

Environment Example

In this exercise, we will create BPEL process using the following environment.

The BPEL Process in this Exercise

In this exercise, you are required to realize the composite back translation service (translate the source from language A to language B and then traslate the result from language B back to language A) by connecting two atomic machine translation services provided by the Language Grid.

The machine translation service used in this exercise is J-Server (Kodensha) provided by the Language Grid.

The back translation service is realized by composing two machine translation services. (Translation service 1: Japanese→English + Translation service 2: English→Japanese)

The specification of the back translation BPEL process is as follows.

Steps for Creating Back Translation BPLE Process

Steps for creating back translation BPLE process using Eclipse BPEL Designer is as follows.

Try More Language Services

You can practice this exercise more by creating back transtion service using more than two intermediate languages at the same time. To achieve this extended exercise, you can use the following language service provided by participants of the Language Grid together with J-Server.