Introduction to WS-BPEL and WSO2 BPS
Kasun Indrasiri
Associate Technical Lead
PMC, Apache Synapse
Member, Integration MC
WSO2 Inc.
May 2013
Agenda
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What is a Business Process / WS-BPEL
WSO2 Business Process Server
Introduction to BPEL
Developing Business Processes with WSO2 Developer Studio
Business Process
• Business process is a set of logically related activities
• These activities are performed in a predefined order to achieve a
business goal
Example process
Orchestration vs. Choreography
• Orchestration
– Business process with central
coordinator
– WS-BPEL
• Choreography
– Business collaboration
WS-BPEL
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Business Process Execution Language
An Oasis standard
XML based language for service composition
BPEL defines xml based grammar for describing the logic to
coordinate and control interactions between Web Services
• Create, Consume and Aggregate services
Why use WS-BPEL
• Increase efficiency of business
– No need to worry about the coordination of the process
• Portable business processes
– Built on top of standard compliant web services infrastructure
• Industry wide language for implementing business processes
– Common skill set
• Native support for long running processes
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– Execute asynchronous processes that takes days to complete
Managed execution
WSO2 Business Process Server
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Executes business processes written using WS-BPEL standard
Powered by Apache ODE ( ode.apache.org )
WS-Human Tasks and BPEL4People
Provides a Management Console to
– View and Manage Processes / Human Tasks
– View and Manage Instances / Tasks
– Configure QOS …
Introduction to WS-BPEL
Want to implement a BPEL Process ?
• You should have some knowledge on
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XML
XML Namespaces
XML Schema
WSDL
XPath
XSLT
Structure of a WSDL
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<types>
<message/>+
<portType><operation>+</portType>
<binding/>+
<service><port/></service>
BPEL Document Structure
<process>
<partnerLinks><partnerLinks>
<variables></variables>
<messageExchanges></messageExchanges>
<correlationSets></correlationSets>
<faultHandlers></faultHandlers>
<compensationHandlers></compensationHandlers>
<eventHandlers></eventHandlers>
(activities)*
</process>
BPEL Process
<process name="NCName" targetNamespace="anyURI"
queryLanguage="anyURI"?
expressionLanguage="anyURI"?
suppressJoinFailure="yes|no"?
exitOnStandardFault="yes|no"?
xmlns="http://docs.oasisopen.org/wsbpel/2.0/process/executable">
</process>
PartnerLinkType
• Characterizes the conversational relationship between two services
• Define the roles played by each of the services in the conversation
<plnk:partnerLinkType name="BuyerSellerLink">
<plnk:role name="Buyer" portType="buy:BuyerPortType" />
<plnk:role name="Seller" portType="sell:SellerPortType" />
</plnk:partnerLinkType>
PartnerLinkType
Seller
Buyer
Invoke Seller
Process
Send
response to
Buyer’s
Callback
Async
Seller
Buyer
Invoke Seller
Partner
Service
Process
Partner
Service
Sync
PartnerLinks
• Define the relationship between the participating web services (
partners ) and the business process
– myrole “business process’s role”
– partnerRole “partner service’s role”
• Associates interfaces (WSDL ports) with roles, using PartnerLinkTypes
Partner Links
Partner Link
• Partner Link Associates with a partner link type
<partnerLinks>
<partnerLink name=“BuyerSellerPL”
partnerLinkType=“BuyerSellerLink”
myRole=“Buyer”
partnerRole=“Seller”/>
</partnerLinks>
• Defines which role should be played by the process itself and the
partner service
Variables
• Variables used by the process to keep the state
• Statically typed via
– WSDL Message Types
– XML Schema Types
– XML Schema elements
• Variables can be “global” to the process or “local” to the scope
Variables
• Assigning values to variables
– When message is received from a partner
– Manipulate variables inside <assign> activity
– Require knowledge about Xpath , XSLT
Activities
• Activities perform the process logic
• Basic Activities
– describe elemental steps in the process behavior
• Structured Activities
– control-flow logic
– may contain other basic or structured activities
Basic Activities
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Receive
Reply
Invoke
Assign
Empty
Compensate
Catch
• Throw
• Rethrow
• Exit
Receive
• Receive messages from an external party
– Could be an external partner or the initiator of the business process
• Acts as the entry point to the process.
• Associated with
– PartnerLink with MyRole
– WSDL operation
– Variable for the incoming message
• createInstance=“yes” to create a new process instance. Otherwise,
the message will be consumed by an already running process instance
Reply
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Sends the response back to the client
Always relates to a “receive” activity
Associated with
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Same PartnerLink for the “receive”
Same operation for the “receive”
Variable for the output message
Invoke
• Used to consume (invoke) partner services
• Associated with
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PartnerLink with at least a “partnerRole”
WSDL operation of the partner service
Input variable
Output variable, if the operation is request-response
Assign
• Used to manipulate variables
Initializing Variables
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Variables contain a piece of XML
Manipulated using XPath
XPath is evaluated on XML
A variable should be initialized before copying values to the internal
elements.
Expected Content
• echoRequest=
<p:echoString xmlns:p="http://echo.services.core.carbon.wso2.org">
<in>HelloWorld</in>
</p:echoString>
• First we should initialize the variable ‘echoRequest’ before copying
the string value “HelloWorld” to it.
• $echoRequest/p:echoString/in
Structured Activities
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Sequence
While
Pick
Flow
Scope
If
ForEach
RepeatUntil
Compensate
Link
Sequence
• Used to define a set of activities to be executed in a strict ordered
sequence
• Can contain both basic and structured activities nested to arbitrary
depth
<sequence standard-attributes>
standard-elements
activity+
</sequence>
• Contained activities are executed in the order they are defined
• Completes when the last activity has completed
Sequence
Flow
• Used to define a set of activities that will execute concurrently
• Further allows synchronization of dependencies between activities
– When one activity finishes, another activity starts
• Directly nested activities are started concurrently as soon as the flow
activity is started
• Flow activity completes when all nested activities complete
Flow
If
• Used to express a service of alternative choices of which exactly one is
executed
– Primary conditional branch specified by condition element
– followed by
• Unlimited number of elseif branches
– Each with its own condition expression
• One else branch
If
Looping
• Looping executes a subset of the process multiple times in a
controlled manner
– ForEach
– repeatUntil
– while
ForEach
While
RepeatUntil
Pick
• Waits for the occurrence of exactly one event from a set of events.
Pick
• Used to have the process wait until one of a set of events is triggered
– Message events via onMessage element
– Alarm events via onAlarm element
• Can be used to initiate a process instance
– If createInstance=“yes” , a new process instance is create upon the reception of
one of a set of possible messages
– Each on message is equivalent to a receive activity with the
createInstance=“yes”
– No alarms are permitted in the case
Scope
• Used to group activities into logically organized sections
– Encapsulates a possibly compensatable, recoverable unit of work
• Provide processing context for
– Variables
– PartnerLinks
– FaultHandlers and Compensation handlers
Scope
Developing BPEL Process
Contents of a BPEL Package
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Process definition file ( .bpel file )
Related WSDL files
Process deployment descriptor ( deploy.xml )
Optional files
– Unified endpoint files ( .epr )
– Service QOS file (services.xml)
– XSL files
Deploy.xml
HelloWorld Sample
• Generate a Synchronous BPEL Process using Developer studio wizard
• Implement ‘assign’ Logic
Invoking an External Partner
Invoking a Partner Service
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Generate BPEL process using the synchronous process template
Add an invoke activity with two assign activities
Create a PartnerLink and PartnerLinkType
Use echo service that comes with the BPS as the external service
Deploy and execute the process
Invoking a Partner Service
Q&A
Thank You