Seminar on Service Oriented Architecture

1Seminar on SOA

Seminar on Service Oriented Architecture

BPELSome notes selected from “Business Process Execution

Language for Web Services” by Matjaz Juric

2Seminar on SOA

We Are Here

Apps &

Info Assets

B u s i n e s s I n n o v a t i o n & O p t i m i z a t i o n S e r v i c e s

Development

Services

I n t e r a c t i o n S e r v i c e s P r o c e s s S e r v i c e s I n f o r m a t i o n S e r v i c e s

P a r t n e r S e r v i c e s B u s i n e s s A p p S e r v i c e s A c c e s s S e r v i c e s

I n t e g r a t e d

e n v i r o n m e n

t f o r d e s i g n

a n d

c r e a t i o n o f

s o l u t i o n

a s s e t s

M o n i t o r ,

m a n a g e

a n d s e c u r e

s e r v i c e s ,

a p p l i c a t i o n

s &

r e s o u r c e s

F a c i l i t a t e s b e t t e r d e c i s i o n - m a k i n g

w i t h r e a l - t i m e b u s i n e s s

i n f o r m a t i o n

E n a b l e s c o l l a b o r a t i o n

b e t w e e n p e o p l e ,

p r o c e s s & i n f o r m a t i o n

O r c h e s t r a t e a n d

a u t o m a t e b u s i n e s s

p r o c e s s e s

C o n n e c t w i t h t r a d i n g

p a r t n e r s

B u i l d o n a r o b u s t ,

s c a l e a b l e , a n d

s e c u r e s e r v i c e s

e n v i r o n m e n t

F a c i l i t a t e s i n t e r a c t i o n s

w i t h e x i s t i n g

i n f o r m a t i o n a n d

a p p l i c a t i o n a s s e t s

E S BF a c i l i t a t e s c o m m u n i c a t i o n b e t w e e n s e r v i c e s

IT Service

Management

I n f r a s t r u c t u r e S e r v i c e s

O p t i m i z e s t h r o u g h p u t ,

a v a i l a b i l i t y a n d p e r f o r m a n c e

M a n a g e s d i v e r s e

d a t a a n d c o n t e n t i n

a u n i f i e d m a n n e r

Apps &

Info Assets


Development

Services



I n t e g r a t e d

e n v i r o n m e n

t f o r d e s i g n

a n d

c r e a t i o n o f

s o l u t i o n

a s s e t s

M o n i t o r ,

m a n a g e

a n d s e c u r e

s e r v i c e s ,


s &

r e s o u r c e s









p r o c e s s e s


p a r t n e r s










IT Service

Management




Apps &

Info Assets

Apps &

Info Assets


Development

Services



I n t e g r a t e d

e n v i r o n m e n

t f o r d e s i g n

a n d

c r e a t i o n o f

s o l u t i o n

a s s e t s

M o n i t o r ,

m a n a g e

a n d s e c u r e

s e r v i c e s ,


s &

r e s o u r c e s









p r o c e s s e s


p a r t n e r s











IT Service

Management




M a n a g e s d i v e r s e

d a t a a n d c o n t e n t i n

a u n i f i e d m a n n e r

From IBM’s High Level Reference Architecture

3Seminar on SOA

BPEL

• Business Process Execution Language• Programming in the large• Processing logic to handle synchronous

and asynchronous messages• Quite different from programming in the

small - different issues to deal with • Structured programming language using while, if else, sequence, flow, …• XPATH used for addressing message parts

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Basics• Developing web services and exposing

functionalities is not sufficient. • Need a way to compose these functionalities in

the right order – a way to define business processes which will make use of the exposed functionalities.

• BPEL allows composition of web services.• BPEL may be used for a long running process.• “Dehydration” is the term used to refer to the

saving of a process state. • Successfully completed processes as well are

saved in the dehydration store.

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Web Service Composition Methods - Orchestration

• A central process takes control over the involved web services and coordinates the execution of different operations on the web services involved in the operation.

• This is done as per the requirements of the orchestration.

• The involved web services do not know (and do not need to know) that they are involved into a composition and that they are a part of a higher business process.

• Only the central coordinator of the orchestration knows this.

• So orchestration is centralized with explicit definitions of operations and the order of invocation of web services.

6Seminar on SOA

Web Service Composition Methods - Choreography

• Choreography does not rely on a central coordinator.

• Each web service involved in the choreography knows exactly when to execute its operations and whom to interact with.

• Choreography is a collaborative effort focused on exchange of messages.

• All participants of the choreography need to be aware of the business process, operations to execute, messages to exchange, and the timing of message exchanges.

• This is a peer-to-peer approach.

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Composing web services to execute business processes

• Orchestration is the more flexible approach compared to choreography: – We know exactly who is responsible for the execution of

the whole business process. – We can incorporate web services, even those that are not

aware that they are a part of a business process. – We can also provide alternative scenarios when faults

occur. • BPEL follows the orchestration paradigm. • Choreography is covered by other standards, such as

WSCI (Web Services choreography Interface) and WS-CDL (Web Services Choreography Description Language).

• Choreography has not gained support from the industry which would be comparable to BPEL.

8Seminar on SOA

Programming in the Large History

• IBM WSFL (Web Service Flow Language) defined in May 2001.• Microsoft XLANG defined around the

same time.• Joint submission to OASIS under the

name BPEL4WS.• OASIS (September 2004) WS-BPEL-2.0.• Has no standard graphical language.• The BPEL process itself is a web service.• BPEL business processes are portable.

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BPEL

• BPEL builds on top of XML and web services.

• It is an XML-based language which supports the web services technology stack, including SOAP, WSDL, UDDI, WS-Reliable Messaging, WS-Addressing, WS-Coordination and WS-Transaction.

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A typical BPEL process

• First, the BPEL business process receives a request.

• To fulfill it, the process then invokes the involved web services and finally responds to the original caller.

• Since the BPEL process communicates with other web services, it relies heavily on the WSDL description of the web services invoked by the composite web service.

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Steps in a Process

• Each step is called an activity. • BPEL supports primitive and

structure activities.• Primitive activities represent basic

constructs and are used for common tasks

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Primitive Activities• Invoking other web services, using <invoke> • Waiting for the client to invoke the business

process through sending a message, using <receive> (receiving a request)

• Generating a response for synchronous operations, using <reply>

• Manipulating data variables, using <assign> • Indicating faults and exceptions, using

<throw> • Waiting for some time, using <wait> • Terminating the entire process, using

<terminate> etc.

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Defining Processes

• Combine these and other primitive activities and define complex algorithms, which exactly specify the steps of business processes.

• To combine primitive activities BPEL supports several structured activities

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Structured Activities

• Sequence ( <sequence>), which allows us to define a set of activities that will be invoked in an ordered sequence

• Flow ( <flow>) for defining a set of activities that will be invoked in parallel

• Case-switch construct ( <switch>) for implementing branches

• While ( <while>) for defining loops • The ability to select one of a number of

alternative paths, using <pick>

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Definitions and Declarations

• BPEL processes will typically declare variables using <variable>

• BPEL processes will typically define partner links using <partnerLink>

• A BPEL process can be synchronous or asynchronous. – A synchronous BPEL process blocks the client (the

one which is using the process) until the process finishes and returns a result to the client.

– An asynchronous process does not block the client. Rather it uses a callback to return the result (if any)

16Seminar on SOA

Example Process• For its clients a BPEL process looks like

any other web service. • When we define a BPEL process, we

actually define a new web service that is a composition of existing services.

• The interface of the new BPEL composite web service uses a set of port types, through which it provides operations like any other web service.

• To invoke a business process described in BPEL, we have to invoke the resulting composite web service.

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Typical Structure (1)<process> <partnerLinks> <partnerLink> <partnerLink> </partnerLinks> <variables> <variable> <variable> </variable> <sequence> <receive> the initial client request </receive>

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Partner Links• BPEL calls the links to all parties it

interacts with as partner links• Partner links can be links to web

services that are invoked by the BPEL process

• Partner links can also be links to clients which invoke the BPEL process

• Each BPEL process has at least one client partner link, because there has to be a client that invokes the BPEL process.

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<flow> make calls in parallel <invoke> a web service </invoke> <invoke> another web service </invoke> </flow>

Typical Structure (2)

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<switch> make decisions <case condition =“…”> <assign> <copy> <from>…<to> </case> <otherwise> <assign> <copy> <from>…<to> </otherwise> </switch> <reply> reply to synchronous caller </sequence></process>

Typical Structure (3)

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Sequential Order of Activities

<process> …. <sequence> Do activities in sequential order. <receive> <invoke> <assign> <invoke> <receive> <invoke> </sequence></process>

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Parallel Activities

<process> …. <sequence> <receive> Wait to start process <flow> <invoke> The three invokes are <invoke> carried out in <invoke> parallel. </flow> </sequence></process>

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Parallel Sequences<process> …. <sequence> <receive> Wait to start process. <flow> Both sequences may run in parallel. <sequence> <invoke> These two ‘invokes’ go in order. <invoke> </sequence> <sequence> <invoke> These two ‘invokes’ go in order <invoke> </sequence> </flow> </sequence></process>

25Seminar on SOA

Synchronous Web Services

The sender blocks and waits for a reply.The service should run fast. The <receive>and <reply> form a pair on B.

<receive>

<invoke>..<invoke>

<reply>

A B

<invoke>

No <receive> needed

B is a synchronousweb service and uses a BPEL reply.

26Seminar on SOA

Quiz on Synchronous Web Services

What does A need to know about B? In otherwords, what is required in B’s WSDL?

<receive>

<invoke>..<invoke>

<reply>

A B

<invoke>

No <receive> needed.B is a synchronousweb service and uses a BPEL reply.

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Quiz on Synchronous Web Services

What does A need to know about B? In otherwords, what is required in B’s WSDL? A needs to know the message types and the availableoperations as well as B’s location.

<receive>

<invoke>..<invoke>

<reply>

A B

<invoke>

No <receive> needed.

B is a synchronousweb service and uses a BPEL reply.

28Seminar on SOA

Asynchronous Web Services (1)

<receive>

<invoke>..<invoke>

<invoke>

A B

Most real-world processes are long running and if callbacks are needed, message correlation may be used.If callbacks are not needed, B need not perform an <invoke>.

<invoke>

Do other things…

<receive> B is an asynchronousweb service andreplies with anoptional “invoke” not a “reply”.

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Quiz on Asynchronous Web Services

<receive>

<invoke>..<invoke>

<invoke>

A B

What does A need to know in order to use B? In other words,what information must be available in B’s WSDL?

<invoke>

Do other things…


30Seminar on SOA

Quiz on Asynchronous Web Services

<receive>

<invoke>..<invoke>

<invoke>

A B

What does A need to know in order to use B? In other words,what information must be available in B’s WSDL? A needs to know the message types and the availableoperations as well as B’s location. In order to use B, A must also know exactly what operations it needsto provide and what messages will be received.

<invoke>

Do other things…


31Seminar on SOA

Example Business Process

Collect employee information (name, id, travel plans, etc.). Determine an employee’s flying status (first class or coach) and then determine the cheaper of two airlines. Return suggestedflight to the employee.

32Seminar on SOA

Modified Example from Juric Text

EmployeeTravel Status WSsynchronous

AmericanAirlines WSasynchronous

DeltaAirlines WSasynchronous

Asynch Process for Business Travels

<invoke>

<receive>

<receive>

<invoke> Coach or first class

<invoke>:<receive><invoke>:<receive>

<invoke> price

price

Asynchronous web service

33Seminar on SOA

Partner Links

• Partner links describe links to partners.

• Partners might be:

(1) Services that invoke the BPEL process. (2) Services invoked by the BPEL process. (3) Services that play both roles - the BPEL process invokes the service and the service invokes a callback on the BPEL process.

34Seminar on SOA

PartnerLinkTypes

• PartnerLinkTypes represent interactions between the parties.

• We have three types of interactions in the airline example: (1) The client interacts with the BPEL process. (2) The BPEL process calls the employee status web service. (3) The BPEL process calls the two airline web services and expects callbacks from both.

35Seminar on SOA

PartnerLinkTypes

• Within the BPEL process WSDL, we have two roles defined for one of the links:

<partnerLinkType name="travelLT">

<role name="travelService"> The interface of the <portType name="tns:TravelApprovalPT" /> BPEL service is implemented </role> at the service.

<role name="travelServiceCustomer"> The interface of the <portType name="tns:ClientCallbackPT" /> client callback is implemented</role> on the client.

</partnerLinkType> travelLTTravel Link Type

BPEL Processinterface

Client callbackinterface

36Seminar on SOA

PartnerLinkTypes

• The employee status WS is synchronous so within the employee status WS WSDL we have one role defined:

<partnerLinkType name="employeeLT">

<role name="employeeTravelStatusService"> <portType name="tns:EmployeeTravelStatusPT" /></role>

</partnerLinkType> Interface of employeestatus web service.

employeeLTEmployee Link Type

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PartnerLinkTypes

• The airline web services are asynchronous and so within the airline WS WSDL’s we have two roles defined:

<partnerLinkType name="flightLT">

<role name="airlineService"> <portType name="tns:FlightAvailabilityPT" /> </role>

<role name="airlineCustomer"> <portType name="tns:FlightCallbackPT" /> </role>

</partnerLinkType>flightLTFlight LinkType

AirlineinterfaceCallee’s

callbackinterface

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PartnerLinks Are in the BPEL (1)<partnerLinks> <partnerLink name="client" partnerLinkType="trv:travelLT" myRole="travelService" partnerRole="travelServiceCustomer"/>

<partnerLink name="employeeTravelStatus" partnerLinkType="emp:employeeLT" partnerRole="employeeTravelStatusService"/>

<partnerLink name="AmericanAirlines" partnerLinkType="aln:flightLT" myRole="airlineCustomer" partnerRole="airlineService"/>

<partnerLink name="DeltaAirlines" partnerLinkType="aln:flightLT" myRole="airlineCustomer" partnerRole="airlineService"/> </partnerLinks>

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PartnerLinks Are in the BPEL(2)<partnerLinks> <partnerLink name="client" partnerLinkType="trv:travelLT" myRole="travelService" partnerRole="travelServiceCustomer"/> : :

</partnerLinks>

This partner link is oftype travelLT. So, twointerfaces are involved.This process is the travelservice part. The partnerimplements the client callbackinterface.

These names are defined in the partner link type section.

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PartnerLinks Are in the BPEL(3)<partnerLinks> : :

<partnerLink name="employeeTravelStatus" partnerLinkType="emp:employeeLT" partnerRole="employeeTravelStatusService"/> : :

</partnerLinks>

This partner link is of type employeeLT.So, one interface isinvolved, that is, theinterface of the employee status webservice.

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PartnerLinks Are in the BPEL(4)

<partnerLinks>

: :


<partnerLink name="DeltaAirlines" partnerLinkType="aln:flightLT" myRole="airlineCustomer" partnerRole="airlineService"/>

</partnerLinks>

Both of these partnerlinks are of typeflightLT. As such, twointerfaces are mentioned.The role of this processis to provide the callback (FlightCallbackPT)and the role the partner is to provide the FlightAvailabilityPT.

42Seminar on SOA


<partnerLinks> <partnerLink name="client" partnerLinkType="trv:travelLT" myRole="travelService" partnerRole="travelServiceCustomer"/>

<partnerLinkType name="travelLT">

<role name="travelService"> The interface of the <portType name="tns:TravelApprovalPT" /> BPEL service is implemented </role> at the service.

<role name="travelServiceCustomer"> The interface of the <portType name="tns:ClientCallbackPT" /> client callback is implemented</role> on the client.

</partnerLinkType>

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<partnerLink name="employeeTravelStatus" partnerLinkType="emp:employeeLT" partnerRole="employeeTravelStatusService"/>

<partnerLinkType name="employeeLT"> <role name="employeeTravelStatusService"> <portType name="tns:EmployeeTravelStatusPT" /> </role>

44Seminar on SOA



<partnerLink name="DeltaAirlines" partnerLinkType="aln:flightLT" myRole="airlineCustomer" partnerRole="airlineService"/>

<partnerLinkType name="flightLT">

<role name="airlineService"> <portType name="tns:FlightAvailabilityPT" /> </role>

<role name="airlineCustomer"> <portType name="tns:FlightCallbackPT" /> </role>

</partnerLinkType>

45Seminar on SOA

Variables in BPEL

<variables>

 <variable name="TravelRequest" messageType="trv:TravelRequestMessage"/>

 <variable name="EmployeeTravelStatusRequest" messageType="emp:EmployeeTravelStatusRequestMessage"/>

 <variable name="EmployeeTravelStatusResponse" messageType="emp:EmployeeTravelStatusResponseMessage"/>

46Seminar on SOA

Variables (2)  <variable name="FlightDetails" messageType="aln:FlightTicketRequestMessage"/>

 <variable name="FlightResponseAA" messageType="aln:TravelResponseMessage"/>

 <variable name="FlightResponseDA" messageType="aln:TravelResponseMessage"/>

 <variable name="TravelResponse" messageType="aln:TravelResponseMessage"/>

</variables>

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BPEL Main Process (1)

<sequence>

 <receive partnerLink="client" portType="trv:TravelApprovalPT" operation="TravelApproval" variable="TravelRequest" createInstance="yes" />

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 <assign> <copy> <from variable="TravelRequest" part="employee"/> <to variable="EmployeeTravelStatusRequest" part="employee"/> </copy> </assign>

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 <invoke partnerLink="employeeTravelStatus" portType="emp:EmployeeTravelStatusPT" operation="EmployeeTravelStatus" inputVariable="EmployeeTravelStatusRequest" outputVariable="EmployeeTravelStatusResponse" />

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 <assign> <copy> <from variable="TravelRequest" part="flightData"/> <to variable="FlightDetails" part="flightData"/> </copy> <copy> <from variable="EmployeeTravelStatusResponse" part="travelClass"/> <to variable="FlightDetails" part="travelClass"/> </copy> </assign>

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 <flow>

<sequence> 

<invoke partnerLink="AmericanAirlines" portType="aln:FlightAvailabilityPT" operation="FlightAvailability" inputVariable="FlightDetails" />

<receive partnerLink="AmericanAirlines" portType="aln:FlightCallbackPT" operation="FlightTicketCallback" variable="FlightResponseAA" />

</sequence>

The receive operationmust occur after the invoke. Hence, thesequence tag isused.

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<sequence> 

<invoke partnerLink="DeltaAirlines" portType="aln:FlightAvailabilityPT" operation="FlightAvailability" inputVariable="FlightDetails" />

<receive partnerLink="DeltaAirlines" portType="aln:FlightCallbackPT" operation="FlightTicketCallback" variable="FlightResponseDA" />

</sequence>

</flow>

Only the flow isdone in parallel. Forthe sequence to complete, the airlinemust respond.

53Seminar on SOA


 <switch>

<case condition="bpws:getVariableData('FlightResponseAA', 'confirmationData','/confirmationData/Price') <= bpws:getVariableData('FlightResponseDA', 'confirmationData','/confirmationData/Price')">

 <assign> <copy> <from variable="FlightResponseAA" /> <to variable="TravelResponse" /> </copy> </assign> </case>

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<otherwise>  <assign> <copy> <from variable="FlightResponseDA" /> <to variable="TravelResponse" /> </copy> </assign> </otherwise> </switch>

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 <invoke partnerLink="client" portType="trv:ClientCallbackPT" operation="ClientCallback" inputVariable="TravelResponse" /> </sequence>

</process>

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Sketch of Working Processsequence receive information from employee assign assign to variable invoke invoke service to determine flying status assign assign result to variable flow Do sequences in parallel sequence invoke call airline A receive get price for ticket sequence invoke call airline B receive get price for ticket switch select cheaper flight invoke inform the employee

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Would this work?sequence receive flow assign invoke assign invoke receive invoke receive switch invoke

No. The previous slide had it right.Here, we have not expressed thesynchronization dependenciesbetween activities.

However, BPEL provides for morecomplex concurrency scenariosusing links. A single link is specifiedwith a source and a target.

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We Need To Add Links

sequence receive flow assign assign before the invoke invoke invoke before the assign assign assign before the two invokes invoke invoke before receive receive receive before the switch invoke invoke before receive receive receive before the switch switch invoke

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Sources and Targets In BPEL

<sequence> <receive> <flow> <assign>… <source linkName = “A”/> </assign> <invoke>…. <target linkName = “A” /> <source linkName = “B” /> Invoke before assign </invoke> <assign> <target linkName = “B” /> <source linkName = “C” /> Assign before the two <source linkName = “D” /> invokes. </assign>

Assign before invoke.

Link names are user definedand should be well chosen.

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Sources and Targets

<invoke> <target linkName = “C”/> <source linkName = “E”/> </invoke> <receive> <target linkName = “E”/> <source linkName = “G”/> </receive> <invoke> <target linkName = “D”/> <source linkName =“F” /> </invoke>

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Sources and Targets

<receive> <target linkName = “F”/> <source linkName = “H”/> </receive> <switch> <target linkName = “G”/> <target linkName = “H”/> </switch> </flow> <invoke>

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Concurrency and Links• The flow tag provides the ability to express synchronization dependencies between activities.• In other words, we can specify what happens and when.• Link definitions are placed within the flow activity. For example,

<flow> <links> <link name = “A”/> <link name = “B” /> </links> :• Every link must be associated with exactly one source and target.• A link’s target activity may only be performed after the source activity has completed.• Transition conditions may be added for additional confusion.

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Seminar on Service Oriented Architecture

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