1. Web Service Orchestration
Emílio Francesquini, Felipe Besson, Leonardo Leite
IME - USP
{emilio, besson, leofl}@ime.usp.br
FISL 12
Porto Alegre, June 29, 2011

2. Service - Definition
• According to W3C, web service:
o Is a software system designed to support machine-to-
machine interaction over a network
o Is described by an interface which is machine readable
(more specific WSDL)
• Other systems can interact with web services through
Soap messages
• The interaction is realized using XML over HTTP, and
other web standards
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3. Examples in the Web
RSS
Google Calendar (CalDAV over HTTP)
can be synchronized with iCal
Amazon Web Services (SOAP ou REST
over HTTP)
o EC2
o S3
o SimpleDB
o ...
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4. Web Services
• Web services have been used to integrate systems,
replacing:
o The use of TCP/IP sockets
o CORBA, JRMI, RPC...
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5. WS – Features
• Any language supporting TCP sockets are ready for using
web services
• The use of HTTP make web services more suitable for
bypassing firewalls, proxies, …
• It is widely accepted by companies
• Loose coupling and the possibility of evolution of the
interface while maintaining backward compatibility
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6. SOAP
• Standard for supporting the interoperability of
heterogeneous systems.
• Since 2003, it is a W3C standard
• In the beginning, Soap was an acronym for Simple Object
Access Protocol
o Then, it was decided that the acronym means
nothing :-)
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7. Message Format
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8. Example of a Soap request
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9. Example of a Soap response
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10. WSDL - Hello world
<?xml version="1.0" encoding="UTF-8"?>
<definitions xmlns:soap=””http://schemas.xmlsoap.org/wsdl/soap/"
xmlns:tns=”http://hello” xmlns:xsd="http://www.w3.org/2001/XMLSchema"
xmlns="http://schemas.xmlsoap.org/wsdl/" targetNamespace="http://hello/"
name="HelloWorldService">
<types>
<xsd:schema>
<xsd:import namespace="http://hello/"
schemaLocatio=”http://localhost:8080/hello?xsd=1"></xsd:import>
</xsd:schema>
</types>
<message name="sayHelloTo">
<part name="parameter" element="tns:sayHelloTo"></part>
</message>
<message name="sayHelloToResponse">
<part name="parameter" element="tns:sayHelloToResponse"></part>
</message>
<portType name="HelloWorld">
<operation name="sayHelloTo">
<input message="tns:sayHelloTo"></input>
<output message="tns:sayHelloToResponse"></output>
</operation>
</portType> 10

11. WSDL Example - Hello world
<binding name="HelloWorldPortBinding" type="tns:HelloWorld">
<soap:binding transport="http://schemas.xmlsoap.org/soap/http”
style="document"></soap:binding>
<operation name="sayHelloTo">
<input>
<soap:body use="literal"></soap:body>
</input>
<output>
<soap:body use="literal"></soap:body>
</output>
</operation>
</binding>
<service name="HelloWorldService">
<port name="HelloWorldPort" binding="tns:HelloWorldPortBinding">
<soap:address location="http://localhost:8080/hello”></soap:address>
</port>
</service>
</definitions> 11

12. Disadvantages
• Messages are too big:
o Low performance during the processing in the client and
the server sides
o Requested Bandwidth is large
o Extremely inefficient when compared to CORBA or JRMI
technologies
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13. WS Composition
• Tipically, a real case of WS Composition involves:
o More than one web service
o Order / interdependence between requests to web
services
o Decision making during the workflow based on the
information obtained so far
o Dealing with services unavailability
o Transaction control
o Business automation
o ...
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14. Web Service Compositions
• Orchestration - Centralized
• Choreography - Distributed
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15. Composition - Example
• Sale system:
o Customer registration
o Charging
• Used in all computers of a store
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16. Solution 1
• I can write the code using my favorite programming
language and then, I integrate the ws client into my
system:
o web services access
o exception handling
• The workflow is defined by myself
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17. Solution 2
• I can copy the code and deploy it with my website
• Now, both website and client share the code containing
the workflow, rules, ….
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18. Problems 1
• Web services are implemented possibly in several languages ​
but the information flow and their relationship get couple to a
specific language
• The developer must deal with:
o Paralelism
o Transaction
o Fault tolerance (e.g., service unavailability)
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19. Problems 2
• Changes in web services, even small ones, involves customers'
upgrade and deployment of new version of the site
• Client/Site can became overloaded due the communication with
the server
• Limitation of devices / code replication..
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20. Solution 3
• A new web service is created
o Containing the entire workflow and composition rules
o Controlling transactions, paralellism and exceptions
handling
• Clients, sites and devices begin to use this web service
directly
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21. However, some problems remain
• Workflow coupled to a specific programming language
• The developer still must deal with the transaction,
parallelism and exceptions handling.
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22. Orchestration
• BPEL – Business Process Execution Language
o 2002
o BPEL4WS – BEA (now Oracle)
o WSFL – IBM
o XLANG – Microsoft
o ... SAP and Siebel Systems.
o 2003 – Open Standard WS-BPEL, by OASIS
o XML with .bpel extension
o Normally called by BPEL when the specific version
does not matter
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23. BPEL
Shin, 2010
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24. Motivations for using BPEL
• A business standard
• Supported by tools, some of them free, for editing and
executing BPEL
o Apache – ODE
o Oracle – OpenESB, NetBeans 6.X
o Active Endpoints – The Active BPEL, ActiveBPEL
Designer
o Microsoft – BizTalk
o Oracle – BPEL Process Manager
o Petalslink – EasyBPEL
• Portability* between different enforcement mechanisms
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25. BPEL Structure
<process ...>
<partnerLinks> ... </partnerLinks>
<variables> ... </variables>
<correlationSets> ... </correlationSets>
<compensationHandlers> ... </compensationHandlers>
<eventHandlers> ... </eventHandlers>
... (activities belonging to the business flow)
</process>
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26. Activities accepted by BPEL
• Basic • Structured
• <invoke> • <if>
• <receive> • <while>
• <reply> • <repeatUntil>
• <assign> • <foreach>
• <throw> • <pick>
• <wait> • <flow>
• <empty> • <sequence>
• <exit> • <scope>
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27. BPEL - synchronous example
<?xml version="1.0" encoding="UTF-8"?>
<process name="SynchronousSample" ...>
<import namespace="http://SynchronousSample"
location="SynchronousSample.xsd"
importType="http://www.w3.org/2001/XMLSchema"/>
<import namespace="http://SynchronousSample"
location="SynchronousSample.wsdl"
importType="http://schemas.xmlsoap.org/wsdl/"/>
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28. BPEL - synchronous example
<partnerLinks>
<partnerLink
name="SynchronousSample"
partnerLinkType="ns1:partnerlinktype1"
myRole="partnerlinktyperole1">
</partnerLink>
</partnerLinks>
<variables>
<variable name="outputVar"
messageType="ns1:responseMessage"/>
<variable name="inputVar"
messageType="ns1:requestMessage"/>
</variables>
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29. BPEL - Exemplo síncrono
<sequence>
<receive name="start" partnerLink="SynchronousSample" operation="operation1"
portType="ns1:portType1" variable="inputVar" createInstance="yes"/>
<assign name="Assign1">
<copy>
<from>concat('Hello ', $inputVar.inputType/ns2:paramA, '!!!')</from>
<to>$outputVar.resultType/ns2:paramA</to>
</copy>
</assign>
<reply name="end" partnerLink="SynchronousSample" operation="operation1"
portType="ns1:portType1" variable="outputVar">
</reply>
</sequence>
</process>
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30. BPEL - synchronous example
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31. BPEL - synchronous example
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32. ESB
• Acronym for Enterprise Service Bus
• The same idea of hardware bus, ESB is charge of:
o transporting,
o routing,
o And messages delivering
• Service access management
• These activities can be performed without an ESB
o The goal of a ESB is just facilitate the work =p
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33. Petals
• Open Source ESB – LGPL 2.1
• Compatible with the standards: JBI and BPEL
• Hot service deployment
• Hot component installation
• Tools to support the development:
o PetalsStudio
o Web Console
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34. Questions?
This research has received founding from:
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35. References
• W3C Web Services Choreography Working Group Charter
• http://www.w3.org/2005/12/wscwg-charter.html
• Web Services Glossary, http://www.w3.org/TR/ws-gloss/
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36. References
• ZHANG, Liang-Jie. Services Computing, Pequim,
Springer, 2007
• Hewitt, Eben, Java SOA Cookbook, 1st Edition, 2009,
• Shin, San, SOA Using OpenESB, BPEL and NetBeans,
2010
• http://ccsl.ime.usp.br/baile
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