BPEL4WS

We describe workflows and the workflow language BPEL4WS. We study the possibility of using workflows in multiagent enactment.

• Andrews et. al. Business Process Execution Language for Web Services Version 1.1 [1]. 2003.
• José M. Vidal, Paul Buhler, and Christian Stahl. Multiagent Systems with Workflows. [2] IEEE Internet Computing, January/February; 8(1):76--82, 2004.

• A representation of how work flows from person to person. Some examples include:
  • Fulfillment of a purchase order.
  • Handling an request for admissions at a University.
  • Handling an insurance claim.
  • Diagnosis and treatment of a patient.

• Workflows are pervasive in the business world.
  • IBM WebSphere MQ Workflow [3].
  • Lotus Workflow [4].
  • Microsoft BizTalk Server [5].
  • SAP [6] has been selling workflow systems for a long time (ERP). SAP NetWeaver [7] integrates them with SOAP (aka Web Services).
• Many of these tools allow “workflow experts” to draw these just as one would draw flowcharts.
• Replace the people with web services (which might, in turn, call a person) and you have a fully automated workflow.
• Workflows tell us how to put together individual web services into a coherent whole.
• With SOAP standardized, my SAP can talk to your BizTalk!

• XML-based standard jointly proposed by Microsoft, IBM, SAP, and others.
• Meant to replace their proprietary formats for storing workflow descriptions.
• Assumes atomic web services are described using WSDL.

• A BPEL4WS document is divided into several parts:
  • <partners> contains a list of the web services invoked as part of the workflow.
  • <variables> used in the workflow.
  • <correlationSets> specifies precedence constraints between invocations.
  • <faultHandlers> are the exception handling routines.
  • <compensationHandler> handles compensation.
  • <eventHandlers> for asynchronous events.

<process name="purchaseOrderProcess" 
         targetNamespace="http://acme.com/ws-bp/purchase"
         xmlns="http://schemas.xmlsoap.org/ws/2003/03/business-process/"
         xmlns:lns="http://manufacturing.org/wsdl/purchase">
   
   <partnerLinks>
      <partnerLink name="purchasing" 
               partnerLinkType="lns:purchasingLT"
               myRole="purchaseService"/>
      <partnerLink name="invoicing" 
               partnerLinkType="lns:invoicingLT"
               myRole="invoiceRequester"
               partnerRole="invoiceService"/>
      <partnerLink name="shipping" 
               partnerLinkType="lns:shippingLT"
               myRole="shippingRequester"
               partnerRole="shippingService"/>
      <partnerLink name="scheduling" 
               partnerLinkType="lns:schedulingLT"
               partnerRole="schedulingService"/>
   </partnerLinks>

   <variables>
      <variable name="PO" messageType="lns:POMessage"/>
      <variable name="Invoice" 
                 messageType="lns:InvMessage"/>
      <variable name="POFault" 
                 messageType="lns:orderFaultType"/>
      <variable name="shippingRequest" 
                 messageType="lns:shippingRequestMessage"/>
      <variable name="shippingInfo" 
                 messageType="lns:shippingInfoMessage"/>
      <variable name="shippingSchedule" 
                 messageType="lns:scheduleMessage"/>
   </variables>

   <faultHandlers>
      <catch faultName="lns:cannotCompleteOrder" 
             faultVariable="POFault">
         <reply   partnerLink="purchasing"
                  portType="lns:purchaseOrderPT" 
                  operation="sendPurchaseOrder"
                  variable="POFault" 
                  faultName="cannotCompleteOrder"/>
      </catch>
   </faultHandlers>
 
   <sequence>

      <receive partnerLink="purchasing" 
               portType="lns:purchaseOrderPT" 
               operation="sendPurchaseOrder" 
               variable="PO">
      </receive>

      <flow>

         <links>
            <link name="ship-to-invoice"/>
            <link name="ship-to-scheduling"/>
         </links>

         <sequence>
            <assign>
               <copy>
                  <from variable="PO" part="customerInfo"/>
                  <to variable="shippingRequest" 
                      part="customerInfo"/>
               </copy>
            </assign>
   
            <invoke  partnerLink="shipping" 
                     portType="lns:shippingPT" 
                     operation="requestShipping"
                     inputVariable="shippingRequest" 
                     outputVariable="shippingInfo">
               <source linkName="ship-to-invoice"/>
            </invoke>

            <receive partnerLink="shipping" 
                     portType="lns:shippingCallbackPT" 
                     operation="sendSchedule"
                     variable="shippingSchedule">
               <source linkName="ship-to-scheduling"/>
            </receive>

         </sequence>

         <sequence>

            <invoke  partnerLink="invoicing" 
                     portType="lns:computePricePT" 
                     operation="initiatePriceCalculation"
                     inputVariable="PO">
            </invoke>
            <invoke  partnerLink="invoicing" 
                     portType="lns:computePricePT" 
                     operation="sendShippingPrice"
                     inputVariable="shippingInfo">
               <target linkName="ship-to-invoice"/>
            </invoke>

            <receive partnerLink="invoicing" 
                     portType="lns:invoiceCallbackPT" 
                     operation="sendInvoice"
                     variable="Invoice"/>

         </sequence>

         <sequence>
            <invoke  partnerLink="scheduling" 
                     portType="lns:schedulingPT" 
                     operation="requestProductionScheduling"
                     inputVariable="PO">
            </invoke>
            <invoke  partnerLink="scheduling" 
                     portType="lns:schedulingPT" 
                     operation="sendShippingSchedule"
                     inputVariable="shippingSchedule">
               <target linkName="ship-to-scheduling"/>
            </invoke>
         </sequence>
      </flow>

      <reply partnerLink="purchasing" 
             portType="lns:purchaseOrderPT" 
             operation="sendPurchaseOrder" 
             variable="Invoice"/>
   </sequence>

</process>

<process name="ncname" targetNamespace="uri" 
         queryLanguage="anyURI"?
         expressionLanguage="anyURI"?
         suppressJoinFailure="yes|no"?
         enableInstanceCompensation="yes|no"?
         abstractProcess="yes|no"?
         xmlns="http://schemas.xmlsoap.org/ws/2003/03/business-process/">

  <partnerLinks>?
    <!-- Note: At least one role must be specified. -->
    <partnerLink name="ncname" partnerLinkType="qname" 
             myRole="ncname"? partnerRole="ncname"?>+
    </partnerLink>
  </partnerLinks>

  <partners>?
     <partner name="ncname">+
      <partnerLink name="ncname"/>+
   </partner>
  </partners>

  <variables>?
    <variable name="ncname" messageType="qname"?
                type="qname"? element="qname"?/>+ 
  </variables>

  <correlationSets>?
    <correlationSet name="ncname" properties="qname-list"/>+
  </correlationSets>

  <faultHandlers>?
    <!-- Note: There must be at least one fault handler or default. -->
    <catch faultName="qname"? faultVariable="ncname"?>*
      activity
    </catch>
    <catchAll>?
      activity
    </catchAll>
  </faultHandlers>

  <compensationHandler>?
    activity
  </compensationHandler>

  <eventHandlers>?
    <!-- Note: There must be at least one onMessage or onAlarm handler. -->
    <onMessage partnerLink="ncname" portType="qname"
               operation="ncname" variable="ncname"?>
      <correlations>?
        <correlation set="ncname" initiate="yes|no"?>+
      <correlations>
      activity
    </onMessage>
    <onAlarm for="duration-expr"? until="deadline-expr"?>*
      activity
    </onAlarm>
  </eventHandlers>
    
  activity
</process>

• Where activity can be any one of:
  • <receive>
  • <reply>
  • <invoke>
  • <assign>
  • <throw>
  • <terminate>
  • <wait>
  • <empty>
  • <sequence>
  • <switch>
  • <while>
  • <pick>
  • <flow>
  • <scope>
  • <compensate>

• The <receive> construct allows the business process to do a blocking wait for a matching message to arrive.

<receive partnerLink="ncname" portType="qname" operation="ncname"
         variable="ncname" createInstance="yes|no"
         standard-attributes>
  standard-elements
  <correlations>?
    <correlation set="ncname" initiate="yes|no"?>+
  </correlations>
</receive>

• We are publishing a web service!

• The <reply> construct allows the business process to send a message in reply to a message that was received through a <receive>.
• The combination of a <receive> and a <reply> forms a request-response operation on the WSDL portType for the process.

<reply partnerLink="ncname" portType="qname" operation="ncname"
       variable="ncname"? faultName="qname"?
       standard-attributes>
  standard-elements
  <correlations>?
     <correlation set="ncname" initiate="yes|no"?>+
  </correlations>
</reply>

• The <invoke> construct allows the business process to invoke a one-way or request-response operation on a portType offered by a partner.

<invoke partnerLink="ncname" portType="qname" operation="ncname"
        inputVariable="ncname"? outputVariable="ncname"?
        standard-attributes>
  standard-elements
  <correlations>?
     <correlation set="ncname" initiate="yes|no"? 
                  pattern="in|out|out-in"/>+
  </correlations>
  <catch faultName="qname" faultVariable="ncname"?>*
    activity
  </catch>
  <catchAll>?
    activity
  </catchAll>
  <compensationHandler>?
    activity
  </compensationHandler>
</invoke>

<!--- for example -->
<invoke partnerLink="Seller" portType="SP:Purchasing" 
        operation="SyncPurchase" 
        inputVariable="sendPO" 
        outputVariable="getResponse">
  <compensationHandler>
      <invoke partnerLink="Seller" portType="SP:Purchasing" 
              operation="CancelPurchase" 
              inputVariable="getResponse"
              outputVariable="getConfirmation">
  </compensationHandler>
</invoke>

• We are invoking a web service!

• The <assign> construct can be used to update the values of variables with new data. An <assign> construct can contain any number of elementary assignments. The syntax of the assignment activity is:

<assign standard-attributes>
  standard-elements
  <copy>+
    from-spec
    to-spec
  </copy>
</assign>

• The <throw> construct generates a fault from inside the business process.

<throw faultName="qname" faultVariable="ncname"? standard-attributes>
  standard-elements
</throw>

• The <wait> construct allows you to wait for a given time period or until a certain time has passed. Exactly one of the expiration criteria must be specified.

<wait (for="duration-expr" | until="deadline-expr") standard-attributes>
  standard-elements
</wait>

• The <empty> construct allows you to insert a "no-op" instruction into a business process. This is useful for synchronization of concurrent activities.

<empty standard-attributes>
  standard-elements
</empty>

• The <sequence> construct allows you to define a collection of activities to be performed sequentially in lexical order.

<sequence standard-attributes>
  standard-elementsactivity+
</sequence>

• The <switch> construct allows you to select exactly one branch of activity from a set of choices.

<switch standard-attributes>
  standard-elements
  <case condition="bool-expr">+
    activity
  </case>
  <otherwise>?
    activity
  </otherwise>
</switch>

<!-- for example -->

<switch xmlns:inventory="http://supply-chain.org/inventory" 
        xmlns:FLT="http://example.com/faults">
  <case condition= "bpws:getVariableProperty(stockResult,level) > 100">
    <flow>
       <!-- perform fulfillment work -->
    </flow>
  </case>
  <case condition="bpws:getVariableProperty(stockResult,level) >= 0">
    <throw faultName="FLT:OutOfStock" 
           variable="RestockEstimate"/>
  </case>
  <otherwise>
    <throw faultName="FLT:ItemDiscontinued"/>
  </otherwise>
</switch>

• The <while> construct allows you to indicate that an activity is to be repeated until a certain success criteria has been met.

<while condition="bool-expr" standard-attributes>
   standard-elementsactivity
</while>

<!-- for example -->

<variable name="orderDetails" type="xsd:integer"/>
    ...
<while condition=
           "bpws:getVariableData(orderDetails) > 100">
  <scope>
    ...
  </scope>
</while>

• The <pick> construct allows you to block and wait for a suitable message to arrive or for a time-out alarm to go off.

<pick createInstance="yes|no"? standard-attributes>
  standard-elements
  <onMessage partnerLink="ncname" portType="qname"
             operation="ncname" variable="ncname"?>+
    <correlations>?
       <correlation set="ncname" initiate="yes|no"?>+
    </correlations>
    activity
  </onMessage>
  <onAlarm (for="duration-expr" | until="deadline-expr")>*
    activity
  </onAlarm>
</pick>
                
<!-- for example -->
<pick>
  <onMessage partnerLink="buyer"
                portType="orderEntry"
                operation="inputLineItem"
                variable="lineItem">
        <!-- activity to add line item to order -->
  </onMessage>
  <onMessage partnerLink="buyer"
                portType="orderEntry"
                operation="orderComplete"
                variable="completionDetail">
        <!-- activity to perform order completion -->
   </onMessage>

   <!-- set an alarm to go after 3 days and 10 hours -->
   <onAlarm for="'P3DT10H'">
        <!-- handle timeout for order completion  -->
   </onAlarm>
</pick>

• The <flow> construct allows you to specify one or more activities to be performed concurrently.

<flow standard-attributes>
  standard-elements
  <links>?
    <link name="ncname">+
  </links>
  activity+
</flow>

<!-- for example -->
<flow>
  <links>
    <link name="XtoY"/>
    <link name="CtoD"/>
  </links>
  <sequence name="X">
     <source linkName="XtoY"/>
     <invoke name="A" .../>
     <invoke name="B" .../>
  </sequence>
  <sequence name"Y">
     <target linkName="XtoY"/>
     <receive name="C" ...>
       <source linkName="CtoD"/>
     </receive>
     <invoke name="E" .../>
  </sequence>
  <invoke partnerLink="D" ...>
    <target linkName="CtoD"/>
  </invoke>
</flow>

• The <scope> construct allows you to define a nested activity with its own associated variables, fault handlers, and compensation handler.

<scope variableAccessSerializable="yes|no" standard-attributes>
    standard-elements
    <variables>?

    </variables>
    <correlationSets>?

    </correlationSets>
    <faultHandlers>?

    </faultHandlers>
    <compensationHandler>?

    </compensationHandler>
    <eventHandlers>?
      ...
    </eventHandlers>
    activity
</scope>
                

• The <compensate> construct is used to invoke compensation on an inner scope that has already completed normally.

<compensate scope="ncname"? standard-attributes>
  standard-elements
</compensate>

• A BPEL4WS workflow is like a class.
• An instance is created when an activity (receive) occurs which has createInstance="yes".
• Every workflow must have at least one such start activity.
• If more than one, they must be correlated using a correlationset.
• The instance dies when either
  1. It reaches the end of the workflow.
  2. It raises a fault.
  3. It is terminated by <terminate>
  4. A compensationHandler is called.

• The partners are the other businesses (web services) the workflow accesses.
• Each partner plays a role:

  <partnerLinkType name="BuyerSellerLink"
          xmlns="http://schemas.xmlsoap.org/ws/2003/05/partner-link/">
    <role name="Buyer">
      <portType name="buy:BuyerPortType"/>
    </role>
    <role name="Seller">
      <portType name="sell:SellerPortType"/>
    </role>
  </partnerLinkType>
  

• Each role is linked to a WSDL PortType.

• You can define properties which are just nicknames for particular xsd types.

<definitions name="properties"
      targetNamespace="http://example.com/properties.wsdl"
      xmlns:tns="http://example.com/properties.wsdl"
      xmlns:txtyp="http://example.com/taxTypes.xsd"
      xmlns:bpws="http://schemas.xmlsoap.org/ws/2003/03/business-process/"
      xmlns="http://schemas.xmlsoap.org/wsdl/">

    <!-- define a correlation property -->
    <bpws:property name="taxpayerNumber"
                               type="txtyp:SSN"/>
    ...
</wsdl:definitions>

• You can define any new variables and assign them parts of messages, or use them to invoke other services.

<complexType name="tAddress">
  <sequence>
    <element name="number" type="xsd:int"/>
    <element name="street" type="xsd:string"/>
    <element name="city" type="xsd:string"/>
    <element name="phone">
      <complexType>
        <sequence>
          <element name="areacode" type="xsd:int"/>
          <element name="exchange" type="xsd:int"/>
          <element name="number" type="xsd:int"/>
        </sequence>
      </complexType>
    </element>
  </sequence>
</complexType>

<element name = "address" type = "tAddress"/>

<!-- this message in the the .wsdl file -->
<message name="person" xmlns:x="http://tempuri.org/bpws/example">
  <part name="full-name" type="xsd:string"/>
  <part name="address" element="x:address"/>
</message>
<!-- -->

<variable name="c1" messageType="x:person"/>
<variable name="c2" messageType="x:person"/>
<variable name="c3" element="x:address"/>

<assign>
  <copy>
    <from variable="c1"/>
    <to variable="c2"/>
  </copy>
  <copy>
    <from variable="c1" part = "address"/>
    <to variable="c3"/>
  </copy>
</assign>                       

• Are used to correlate invoce, receive, and reply activities.
• The correlation sets must first be declared:

  <correlationSets 
         xmlns:cor="http://example.com/supplyCorrelation.wsdl">
      <!-- Order numbers are particular to a customer, 
           this set is carried in application data -->
    <correlationSet name="PurchaseOrder"
              properties="cor:customerID cor:orderNumber"/>
      <!-- Invoice numbers are particular to a vendor, 
           this set is carried in application data -->
    <correlationSet name="Invoice"
              properties="cor:vendorID cor:invoiceNumber"/>
  </correlationSets>
  

  so they can then be used

  <receive partnerLink="Buyer" portType="SP:PurchasingPT" 
           operation="AsyncPurchase" 
           variable="PO">
     <correlations>
       <correlation set="PurchaseOrder" initiate="yes">
     </correlations>
  </receive>
  
  <invoke partnerLink="Buyer" portType="SP:BuyerPT" 
         operation="AsyncPurchaseResponse" inputVariable="POResponse">
     <correlations>
       <correlation set="PurchaseOrder" initiate="no" pattern="out">
       <correlation set="Invoice" initiate="yes" pattern="out">
     </correlations>
  </invoke>
  

• The initiate="yes" means that the correlation is being started (new instance).
• The pattern tells us if the correlation applies to the outbound (request) message, the inbound (response) message, or both.

• links have a name.
• Activities then have source, and target which name particular links.
• Picture each activity as a node, the links are directed links from the source activity to the target activity.
• The links signify temporal precedence.

<process name="loanApprovalProcess" 
         targetNamespace="http://acme.com/loanprocessing" 
         xmlns="http://schemas.xmlsoap.org/ws/2003/03/business-process/"
         xmlns:lns="http://loans.org/wsdl/loan-approval"
         suppressJoinFailure="yes">

   <partnerLinks>
      <partnerLink name="customer" 
               partnerLinkType="lns:loanPartnerLinkType"
               myRole="loanService"/>
      <partnerLink name="approver" 
               partnerLinkType="lns:loanApprovalLinkType"
               partnerRole="approver"/>
      <partnerLink name="assessor" 
               partnerLinkType="lns:riskAssessmentLinkType"
               partnerRole="assessor"/>
   </partnerLinks>

   <variables>
     <variable name="request" 
                messageType="lns:creditInformationMessage"/>
     <variable name="risk" 
                messageType="lns:riskAssessmentMessage"/>
     <variable name="approval" 
                messageType="lns:approvalMessage"/>
     <variable name="error" 
                messageType="lns:errorMessage"/>
   </variables>

   <faultHandlers>
      <catch faultName="lns:loanProcessFault" 
             faultVariable="error">
         <reply   partnerLink="customer"
                  portType="lns:loanServicePT" 
                  operation="request"
                  variable="error" 
                  faultName="unableToHandleRequest"/>
      </catch>
   </faultHandlers>
                                                                  

   <flow>

      <links>
         <link name="receive-to-assess"/>
         <link name="receive-to-approval"/>
         <link name="approval-to-reply"/>
         <link name="assess-to-setMessage"/>
         <link name="setMessage-to-reply"/>
         <link name="assess-to-approval"/>
      </links>

      <receive partnerLink="customer" 
               portType="lns:loanServicePT" 
               operation="request" 
               variable="request" createInstance="yes">
         <source linkName="receive-to-assess"
            transitionCondition=
              "bpws:getVariableData('request','amount')< 10000"/>          
         <source linkName="receive-to-approval"
            transitionCondition=
              "bpws:getVariableData('request','amount')>=10000"/>
      </receive>

      <invoke  partnerLink="assessor" 
               portType="lns:riskAssessmentPT" 
               operation="check"
               inputVariable="request"  
               outputVariable="risk">
         <target linkName="receive-to-assess"/>
         <source linkName="assess-to-setMessage" 
            transitionCondition=
              "bpws:getVariableData('risk','level')='low'"/>
         <source linkName="assess-to-approval" 
            transitionCondition=
              "bpws:getVariableData('risk','level')!='low'"/>
      </invoke>

      <assign>
         <target linkName="assess-to-setMessage"/>
         <source linkName="setMessage-to-reply"/>
         <copy>
            <from expression="'yes'"/>
            <to variable="approval" part="accept"/>
         </copy>
      </assign>

      <invoke  partnerLink="approver" 
               portType="lns:loanApprovalPT" 
               operation="approve" 
               inputVariable="request" 
               outputVariable="approval">
         <target linkName="receive-to-approval"/>
         <target linkName="assess-to-approval"/>
         <source linkName="approval-to-reply" />
      </invoke>

      <reply   partnerLink="customer" 
               portType="lns:loanServicePT" 
               operation="request" 
               variable="approval">
         <target linkName="setMessage-to-reply"/>
         <target linkName="approval-to-reply"/>
      </reply>
   </flow>

</process>
                

• Current workflow enactment tools are centralized.
• BPEL4WS is centralized.
• BPEL4WS does not allow for any deviation or replacements. Web services are not autonomous.
• We are studying ways to do adaptive multiagent enactment of workflows.
  • Enact one workflow as a multiagent system, using Petri Nets. Buhler's thesis provides the first proof of concept.
  • Add autonomous agents.
  • Instantiate thousands of partial workflows under uncertainty. If many workflows will fail, how does the agent choose which one to participate in?
  • Mechanism design issues: what incentives should we provide agents in order to implement a successful business workflow?