1. Web Services (NSWI145)
Lecture 09: WS BPEL
Martin Nečaský, Ph.D.
Faculty of Mathematics and Physics
Charles University in Prague, Czech Republic
Summer 2013

2. Core WS Technologies
 SOAP
 defines XML messaging protocol for basic web
service interoperability
 WSDL
 introduces common grammar for describing web
services
Summer 2013

3. Business Process Automation
 ordering of activities with beginning and end
performed to achieve business outcome
 has inputs and outputs
Summer 2013

4. Business Process Automation
 WSDL provides only stateless model for
particular
 request-response message exchange, or
 uncorrelated one-way message exchange
 typical model of business interaction
 sequence of particular peer-to-peer message
exchanges
• request-response and/or one-way
 stateful, long running interactions involving two or
more parties
Summer 2013

5. Business Process Automation
 core WS technologies allow automation of
only particular message exchange
 we need additional WS technologies to
support automation of whole business
processes
 core terms
 WS orchestration
 WS choreography
Summer 2013

6. WS Orchestration
 specifies an executable process
 result is a web service
 view of one party that controls the process
 WS-BPEL: Web Services Business Process
Execution Language
Summer 2013

7. WS Choreography
 specifies a sequence of messages between collaborating
partners and resources
 how they should communicate with each other
 not an executable process
 no particular view of particular partner
 WS-CDL: Web Services Choreography Description
Language
Summer 2013

8. BPEL
 XML based language for orchestrating Web
Services
 BPEL has two parts
 extensions to WSDL
 business process execution constructs
 BPEL script (internal process specification) +
WSDL document (external process specification)
 define new Web Service implemented as
orchestration of other Web Services
 requires WSDL 1.1 (WSDL 2.0 not supported)
Summer 2013

9. Sample Process
Receive Purchase Order
Send Invoice
Check Credit Card
Process Payment
Calculate Purchase
Order Price
Arrange Logistics
Summer 2013

10. BPEL
 BPEL process = Abstract Web Service
 has WSDL description
• port types composed of operations with inputs and
outputs
• operates only on the level of WSDL portTypes
– no binding to concrete services specified by WS-BPEL process
description
 orchestrates other web services
Summer 2013

11. Process Exposition with WSDL
 exposes BPEL process as a web service
described with WSDL
 WSDL 1.1 file with few restrictions and
extensions
 restrictions
• no service and binding is defined
• only types, messages, port types with operations
Summer 2013

12. Process Exposition with WSDL
PurchaseOrder
Process
PurchaseOrder
PortType
sendPurchaseOrder
Operation
Customer
Purchase Order
Invoice
Summer 2013

13. Process Exposition with WSDL
<wsdl:description targetNamespace="http://purchase" ...>
...
<wsdl:portType name="PurchaseOrderPortType">
<wsdl:operation name="sendPurchaseOrderOperation">
<wsdl:input name="pos:PurchaseOrder" />
<wsdl:output name="pos:Invoice" />
</wsdl:operation>
</wsdl:portType>
</wsdl:description>
Summer 2013

14. Process Exposition with WSDL
 WSDL 1.1 file with few restrictions and
extensions
 extensions
• partner link type
– characterization of conversational relationships between
process and its partner
• partner link type between process and web service
utilized by process
– two participants (process and web service) each with own role
• partner link type between process and its client
– one participant (process) with own role
Summer 2013

15. CreditCard
Service
CreditCard
PortType
checkCreditCard
Operation
Process Exposition with WSDL
PurchaseOrder
Process
CreditCardCallback
PortType
processPayment
Operation
confirmCreditCard
Operation
CreditCardConfirmation
confirmPayment
Operation
PaymentConfirmation
partner link
type
CreditCard
Payment
Summer 2013

16. Process Exposition with WSDL
<wsdl:description targetNamespace="http://purchase" ...>
...
<wsdl:portType name="CreditCardCallbackPortType">
<wsdl:operation name="confirmCreditCardOperation">
<wsdl:input name="cc:CreditCardConfirmation" />
</wsdl:operation>
<wsdl:operation name="confirmPaymentOperation">
<wsdl:input name="cc:PaymentConfirmation" />
</wsdl:operation>
</wsdl:portType>
</wsdl:description>
Summer 2013

17. Process Exposition with WSDL
<wsdl:description
targetNamespace="http://creditcard" ...>
...
<wsdl:portType name="CreditCardPortType">
<wsdl:operation name="checkCreditCardOperation">
<wsdl:input name="cc:CreditCard" />
<wsdl:output name="cc:CreditCardConfirmation" />
</wsdl:operation>
<wsdl:operation name="processPaymentOperation">
<wsdl:input name="cc:Payment" />
<wsdl:output name="cc:PaymentConfirmation" />
</wsdl:operation>
</wsdl:portType>
</wsdl:description>
Summer 2013

18. Process Exposition with WSDL
 element partnerLinkType
 WSDL extension
 specifies WSDL port types the process offers to and requires
from a partner service
 attribute name
• unique name of the partner link type within the scope of the
WSDL description
 two (typically) or one element role
• each specifies role one of the communicating services acts
• attribute name
– unique name of the role within the partner link type
• attribute portType
– specifies WSDL port type the service acting in this role must offer
Summer 2013

19. Process Exposition with WSDL
<wsdl:description xmlns:plnk =
"http://docs.oasis-open.org/wsbpel/2.0/plnktype">
...
<plnk:partnerLinkType name="CreditCardLinkType">
<plnk:role name="CreditCardServiceRole"
portType="cc:CreditCardPortType" />
<plnk:role name="CreditCardClientRole"
portType="pos:CreditCardCallbackPortType" />
</plnk:partnerLinkType>
</wsdl:description>
Summer 2013

20. Process Exposition with WSDL
<wsdl:description xmlns:plnk =
"http://docs.oasis-open.org/wsbpel/2.0/plnktype">
...
<plnk:partnerLinkType name="PurchaseOrderRequestLinkType">
<plnk:role name="PurchaseOrderServiceRole"
portType="pos:PurchaseOrderPortType" />
</plnk:partnerLinkType>
</wsdl:description>
Summer 2013

21. Process Definition
 root element process with four major sections:
 partnerLinks section
• relationships from process to external partner services
 variables section
• declaration of process data
 faultHandlers section
• handlers for processing faults
 main activity
• activity to be executed by the process
Summer 2013

22. Process Exposition with WSDL
<process xmlns =
"http://docs.oasis-open.org/wsbpel/2.0/
process/executable">
<partnerLinks>...</partnerLinks>
<variables>...</variables>
<faultHandlers>...</faultHandlers>
<!–- {MAIN ACTIVITY} -->
</process>
Summer 2013

23. Process Definition – Partner Link
 specified by element partnerLink
 models a link between the process and a
partner service
 instance of a partner link type
 attribute name
 unique name of the partner link within the
process
 attribute partnerLinkType
 reference to the partner link type
Summer 2013

24. Process Definition – Partner Link
 attribute myRole
 references the role in the partner link type acted
by the process
 attribute partnerRole
 references the role in the partner link type acted
by the partner service
Summer 2013

25. Process Definition – Partner Link
<process>
<partnerLinks>
<partnerLink name="CreditCardLink"
partnerLinkType="pos:CreditCardLinkType"
myRole="CreditCardClientRole"
partnerRole="CreditCardServiceRole" />
...
</partnerLinks>
...
</process>
Summer 2013

26. Process Definition – Partner Link
<process>
<partnerLinks>
...
<partnerLink name="PurchaseOrderRequestLink"
partnerLinkType="pos:PurchaseOrderRequestLinkType"
myRole="PurchaseOrderServerRole" />
...
</partnerLinks>
...
</process>
Summer 2013

27. Process Definition – Variable
 element variable
 variables hold data that constitute the state of the
process
 attribute name
• unique variable name
 content type of the variable specified as WSDL
message type, XSD element or XSD simple/complex
type
• attribute messageType
– reference to WSDL message type
• attribute element
– reference to XSD element declaration
• attribute type
– reference to XSD simple/complex type definition
Summer 2013

28. Process Definition – Variable
<process>
<variables>
<variable name="PurchaseOrderMessage"
messageType="pos:PurchaseOrder" />
<variable name="CreditCardMessage"
messageType="cc:CreditCard" />
<variable name="CreditCardConfirmationMessage"
messageType="cc:CreditCardConfirmation" />
<variable name="InvoiceMessage"
messageType="pos:Invoice" />
... </variables>
... </process>
Summer 2013

29. Process Definition - Activities
 specify the process itself (main activity) or fault handling
 several types of activities:
 messaging activities
• invoke, receive, reply, assign, …
 structured activities
• sequence, flow, if, while, …
 fault activities
• throw, exit, …
 compensation activities
• compensate, …
Summer 2013

30. Process Definition – invoke
 allows business process to call a partner service
 invokes one-way or request-response operation on a partner's port
type
 attribute partnerLink
 specifies invoked partner port type
 attribute operation
 specifies invoked operation of the partner port type
 attribute inputVariable
 specifies variable with the input message
 can be replaced by toParts element with toPart child elements if
the input message has more parts
 attribute outputVariable
 specifies variable with the output message
 can be replaced by fromParts element with fromPart child
elements if the output message has more parts
Summer 2013

31. Process Definition – invoke
<process>
<invoke
name="CreditCardCheckInvoke"
partnerLink="CreditCardLink"
operation="checkCreditCard"
inputVariable="CreditCardMessage"
outputVariable="CreditCardConfirmationMessage" />
</process>
Summer 2013

32. Process Definition – receive
 allows business process to receive a message
from a partner service
 blocking activity
 attribute partnerLink
 specifies port type of the process that is awaited
to be invoked by the partner
 attribute operation
 specifies operation of the port type that is awaited
to be invoked by the partner
Summer 2013

33. Process Definition – receive
 attribute variable
 specifies variable where the arrival message will
be assigned
 attribute createInstance
 "yes"/"no" value
 if "yes" the activity creates new process
instance
Summer 2013

34. Process Definition – receive
<process>
<receive
name="PurchaseOrderRequestFromCustomer"
partnerLink="PurchaseOrderRequestLink"
operation="processPurchaseOrder"
variable="PurchaseOrderMessage"
createInstance="yes" />
</process>
Summer 2013

35. Process Definition – reply
 allows business process to send a message in
a reply to a message that was received by
receive
 similar structure to invoke
Summer 2013

36. Process Definition – reply
<process>
<reply
name="InvoiceReplyToCustomer"
partnerLink="PurchaseOrderRequestLink"
operation="processPurchaseOrder"
variable="InvoiceMessage" />
</process>
Summer 2013

37. Process Definition – receive/reply
 implements request/response message
exchange pattern
 it is a pair
 if there are more pairs, distinguish them by
attribute messageExchange
Summer 2013

38. Process Definition – assign
 allows updating values of variables with new
data
 copying data from one variable to another
 construct new data and copy them to a variable
 type validity checked
 element copy
 element from
 element to
Summer 2013

39. Process Definition – assign
 several variants of from and to:
1. from variable to variable
<assign>
<copy>
<from variable="c1" />
<to variable="c2" />
</copy>
</assign>
Summer 2013

40. Process Definition – assign
 several variants of from and to:
2. from variable part to variable
<assign>
<copy>
<from>$c1/lines/line[1]</from>
<to variable="c2" />
</copy>
</assign>
Summer 2013

41. Process Definition – assign
 several variants of from and to:
3. from XSLT script to variable
<assign>
<copy>
<from>bpel:doXslTransform(".../t.xsl", $c1)</from>
<to variable="c2" />
</copy>
</assign>
Summer 2013

42. Process Definition – sequence
 specifies activities to be performed
sequentially
Summer 2013

43. Process Definition – sequence
<process>
<sequence>
<receive name="PurchaseOrderRequestFromCustomer" ... />
<assign>
<copy>
<from>$PurchaseOrderMessage/creditCard</from>
<to variable="CreditCardMessage" />
</copy>
</assign>
<invoke name="CreditCardCheckInvoke" ... />
<assign>...</assign>
<reply name="InvokeReplyToCustomer />
</sequence> </process>
Summer 2013

44. Process Definition – flow
 specifies one or more activities to be
performed concurrently
Summer 2013

45. Process Definition – flow
<process>
<flow>
<sequence>
<invoke name="CreditCardCheckInvoke" ... />
<invoke name="ProcessPaymentInvoke" ... />
</sequence>
<invoke name="CalculatePriceInvoke" ... />
<invoke name="LogisticsInvoke" ... />
</flow>
</process>
Summer 2013

46. Process Definition – flow
 element link
 declares synchronization dependency for flow
 attribute name
• identifies dependency within flow
Summer 2013

47. Process Definition – flow
<process>
<flow>
<links>
<link name="PriceToPaymentLink" />
</links>
...
</flow>
</process>
Summer 2013

48. Process Definition – flow
 each activity may contain sources with one or more
source and targets with one or more target
 establish synchronization relations via links
 element source
 attribute linkName - specifies that the activity is source
activity of the link
 element target
 attribute linkName - specifies that the activity is target
activity of the link
Summer 2013

49. Process Definition – flow
 for a given link, its target activities must wait
until its source activities have finished
Summer 2013

50. Process Definition – flow
<process>
<flow>
...
<invoke name="CalculatePriceInvoke" ... >
<sources>
<source name="PriceToPaymentLink" />
</sources>
</invoke>
...
</flow>
</process>
Summer 2013

51. Process Definition – flow
<process>
<flow>
...
<sequence>
<invoke name="CreditCardCheckInvoke" ... />
<invoke name="ProcessPaymentInvoke" ... >
<targets>
<target name="PriceToPaymentLink" />
</target>
</invoke>
</sequence>
...
</flow>
</process>
Summer 2013

52. Process Definition – flow
 element joinCondition in targets
 contains logical expression specifying waiting
condition
Summer 2013

53. Process Definition – flow
<flow>
<links>...</links>
<sequence name="W">
<targets>
<joinCondition>$XtoW and $YtoW</joinCondition>
<target linkName="XtoW" />
<target linkName="YtoW" />
</targets>
...
</sequence>
</flow>
Summer 2013

54. Process Definition – flow
 element transitionCondition in
source
 contains logical expression specifying condition for
setting the link to true (additional condition to
"being finished")
Summer 2013

55. Process Definition – flow
<flow>
<links>...</links>
<sequence name="X">
<sources>
<source linkName="XtoV">
<transitionCondition>$c &gt; 1000</transitionCondition>
</source>
<source linkName="XtoW">
<transitionCondition>$c &le; 1000</transitionCondition>
</source>
</sources>
...
</sequence>
</flow>
Summer 2013

56. Process Definition – scope
 allows definition of local partner
links, variables and activities
Summer 2013

57. Process Definition – if
 used to select exactly one activity from given branches
 branch = activity
 first branch is directly as child
 element condition
 contains logical expression
 condition for first branch activity
 element elseif
 element condition
 other branch activity under a condition
 element else
 last branch
Summer 2013

58. Process Definition – if
<if>
<invoke>...</invoke>
<condition>$PaymentMessage/price &gt; 1000</condition>
<elseif>
<invoke>...</invoke>
<condition>$PaymentMessage/price&gt;500</condition>
</elseif>
<else>
<invoke>...</invoke>
</else>
</if>
Summer 2013

59. Process Definition – while
 used to define that the child activity is to be
repeated as long as the specified condition is
true
 element condition
 contains logical expression
Summer 2013

60. Process Definition – while
<while>
<condition>$c1 &gt; 1000</condition>
<sequence>
<invoke>...</invoke>
<assign>
<from>...</from>
<to>$c1</to>
</assign>
</sequence>
</while>
Summer 2013

61. Process Definition – forEach
 iterates its child scope exactly N+1 times
where N is given by finalCounterValue
child element minus startCounterValue
child element
 iterated activity is in the child scope
 attribute parallel
 "yes"/"no" value
 if "yes" iterations are performed in parallel
  flow with N+1 activities each for one iteration
Summer 2013

62. Process Definition – forEach
<forEach parallel="yes" countername="n">
<startCounterValue>1</startCounterValue>
<finalCounterValue>
count($PurchaseOrder//item)
</finalCounterValue>
<scope>
... variable $n with actual counter value ...
... iterated activity ...
</scope>
</forEach>
Summer 2013

63. Advanced Concepts
 not presented in this lecture:
 fault handling
 event handling
 terminating processes
 undoing completed work (i.e. compensations)
 message correlation
 dynamic partner resolution
 abstract processes
Summer 2013