XML.gov Working Group

1
Introduction to Business Process Execution
Language for Web Services (BPEL4WS)
Joseph M. Chiusano Booz Allen Hamilton
XML.gov Working Group Washington, DC February
18, 2004
2
Overview

• Introduction
• Partner Links
• Main BPEL4WS Process Flow Constructs
• Message Correlation
• Process Compensation
• Questions

3
Introduction
4
BPEL4WS (Business Process Execution Language For
Web Services) provides a language for the formal
specification of business process behavior based
exclusively on Web Services

• BPEL4WS extends the Web Services interaction
  model and enables it to support business
  transactions
• It defines a model and grammar for describing the
  behavior of a business process based on
  interactions between the process and its partners
• The BPEL4WS specification was originally authored
  by IBM, Microsoft, BEA Systems, SAP, and Siebel
  Systems
• The most current public version is Version 1.1
  (May 2003)
• http//www-106.ibm.com/developerworks/webservices
  /library/ws-bpel/
• The OASIS WS BPEL Technical Committee is
  advancing the BPEL4WS Specification
• Updated version planned for release in
  February/March 2004

5
BPEL4WS sits at the top of the emerging Web
Services stack, at the process/collaboration
modeling layer

• BPEL4WS sits above Web Services Choreography
  definitions

Process/Collaboration Modeling Definitions
Web Services Choreography Definitions
Current Web Services Stack
6
The BPEL4WS process model is layered on top of
the service model defined by WSDL 1.1

• WSDL specifies a hierarchy for describing Web
  Services characteristics in an abstract form

7
BPEL4WS is capable of modeling complex business
processes, and the dependencies between activities

• The following is a BPEL4WS process for handling a
  purchase order

message
Source BPEL4WS Version 1.1 Specification
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Partner Links
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Partner links are used to represent interactions
between a service and each of the parties with
which it interacts

• Partner links define the messages and port types
  used in the interactions in both directions,
  along with role names

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Main BPEL4WS Process Flow Constructs
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The receive, flow and reply constructs are
the main BPEL4WS constructs used to represent
process flows

• The purchase order example uses all three
  constructs

12
The receive, flow and reply constructs are
the main BPEL4WS constructs used to represent
process flows (contd)

• The receive construct allows a process to do a
  blocking wait for a matching message to arrive
• ltreceive partnerLink"purchasing"
• portType"lnspurchaseOrderPT"
• operation"sendPurchaseOrder"
• variable"PO"gt
• lt/receivegt
• The flow construct allows one or more activities
  to be performed concurrently

Wait to receive a purchase order on the
Purchasing partner link
Represents the purchase order message
Source SOAP 1.1 Recommendation
13
The receive, flow and reply constructs are
the main BPEL4WS constructs used to represent
process flows (contd)

• The reply construct allows a process to send a
  message in reply to a message that was received
  through a ltreceivegt
• ltreply partnerLink"purchasing"
• portType"lnspurchaseOrderPT"
• operation"sendPurchaseOrder"
• variableInvoice"gt
• lt/replygt

Send invoice on the Purchasing partner link
Represents the invoice message
Source SOAP 1.1 Recommendation
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BPEL4WS is also capable of modeling dependencies
between activities

• There are several dependencies in the purchase
  order example

Cannot complete production scheduling until
shipping logistics are arranged
Cannot complete price calculation until shipper
is determined
Source BPEL4WS Version 1.1 Specification
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The synchronization dependencies between
concurrent tasks are expressed by using links
to connect them

• The following represents the dependency of the
  price calculation on the shipper selected
• ltinvoke partnerLinkshipping"
• portType"lnsshippingPT"
• operationrequestShipping"
• inputVariable"shippingRequest"gt
• outputVariable"shippingInfo"gt
• ltsource linkName"ship-to-invoice"/gt
• lt/invokegt
• ltinvoke partnerLinkinvoicing"
• portType"lnscomputePricePT"
• operationsendShippingPrice"
• inputVariable"shippingInfo"gt
• lttarget linkName"ship-to-invoice"/gt
• lt/invokegt

This represents the Decide on Shipper activity
This represents the Complete Price Calculation
activity
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Message Correlation
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Message correlation involves the association of
two or more messages with each other in an
asynchronous environment

• This may be done by associating contents in a
  given message with its correlating message
• For example, in a purchase order/invoice
  scenario, the invoice may contain the
  corresponding purchase order number

Source SOAP 1.1 Recommendation
18
BPEL4WS represents message correlations using
correlation sets

• A correlation set contains a set of properties
  shared by all messages in a correlated group
• ltinvoke partnerLink"Buyer" portType"SPBuyerPT"
  
• operation"AsyncPurchaseResponse"
  inputVariable"POResponse"gt
• ltcorrelationsgt
• ltcorrelation set"PurchaseOrder"
  initiate"no" pattern"out"gt
• ltcorrelation set"Invoice"
  initiate"yes" pattern"out"gt
• lt/correlationsgt
• lt/invokegt
• ltcorrelationSet name"PurchaseOrder"
• properties"corcustomerID cororderNumber"/gt
• ltcorrelationSet name"Invoice"
• properties"corvendorID corinvoiceNumber"/gt

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Endpoint References
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BPEL4WS uses endpoint references for dynamic
selection of service providers and invocation of
their operations

• The relevant information about a partner service
  can be set up as part of business process
  deployment
• This is a more static approach
• However, it is also possible to select and assign
  partner services dynamically
• BPEL4WS leverages the WS-Addressing specification
  for this capability
• WS-Addressing defines a standard representation
  for endpoint references that incorporates
  information from a WSDL description as well as
  policy information
• ltwsaEndpointReference xmlnswsa"..."gt
• ltwsaAddressgthttp//www.someendpoint.comlt/wsa
  Addressgt
• ltwsaPortTypegtPurchaseOrderPortTypelt/wsaPortTy
  pegt
• lt/wsaEndpointReferencegt
• URL http//msdn.microsoft.com/ws/2003/03/ws-addre
  ssing

The portType associated with the address
21
Process Compensation
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Business processes are often of long duration,
which means that a business process may need to
be cancelled after many transactions have been
committed during its progress

• Consider a situation in which a user cancels a
  purchase order
• In this situation, it is not possible to lock
  system resources (ex database records) for
  extended periods of time
• Therefore, the partial work must be undone as
  best as possible

User Cancels!
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BPEL4WS defines compensation handlers that are
invoked to perform compensation activities

• A compensation handler is essentially a wrapper
  for compensation activities
• Specifies a compensating operation on a given
  portType for a given partner link
• ltcompensationHandlergt
• ltinvoke partnerLink"Seller"
• portType"SPPurchasing"
• operation"CancelPurchase"
• inputVariable"getResponse"
• outputVariable"getConfirmation"gt
• ltcorrelationsgt
• ltcorrelation set"PurchaseOrder"
• pattern"out"/gt
• lt/correlationsgt
• lt/invokegt
• lt/compensationHandlergt

The CancelPurchase operation invokes a
cancellation
The response to the purchase request is used as
input
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Questions?
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Contact Information

• Joseph M. Chiusano
• Booz Allen Hamilton
• McLean, VA
• [phone]
• chiusano_joseph_at_bah.com