By Matjaz B. Juric

Each BPEL process consists of the following: (a) BPEL code, which defines the orchestration flow; (b) WSDL interface, which defines the interface (and the related XML Schemas) of the BPEL process for its clients; (c) WSDL interfaces of the consumed services (partner links). Partner links define the relations between BPEL process and the web services. Figure 1 shows the overall structure of a 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">
<extensions/>?
<import/>*
<partnerLinks/>?
<messageExchanges/>?
<variables/>
<correlationSets/>?
<faultHandlers/>?
<eventHandlers/>?
activity
</process>

<plnk:partnerLinkType>

Characterizes a relationship between two services. We define roles played by each of the services. We specify the used portType of each service within the context of the conversation. Each <role> specifies exactly one WSDL portType. <plnk:partnerLinkType> is defined in the service WSDL document, not in the BPEL.

<wsdl:definitions name="NCName" targetNamespace="anyURI" ...>
...
<plnk:partnerLinkType name="NCName">
<plnk:role name="NCName" portType="QName" />
<plnk:role name="NCName" portType="QName" />?
</plnk:partnerLinkType>
...
</wsdl:definitions>

Example:

<plnk:partnerLinkType name="OrderLT">
<plnk:role name="OrderService" portType="ord:OrderPT" />
<plnk:role name="OrderRequester" portType="ord:OrderCallbackPT" />
</plnk:partnerLinkType>

<partnerLink>

Defines the relation of the BPEL process to partner web services. For request-reply semantics specify both roles, for one-way semantics specify one role only.

<partnerLinks>?
<!-- At least one role must be specified. -->
<partnerLink name="NCName"
partnerLinkType="QName"
myRole="NCName"?
partnerRole="NCName"?
initializePartnerRole="yes|no"?>+
</partnerLink>
</partnerLinks>

Example:

<partnerLinks>
<partnerLink name="Ordering"
partnerLinkType="tns:OrderLT"
myRole="OrderRequester" partnerRole="OrderService" />
</partnerLinks>

<sref:service-ref>

Endpoint references associated with partnerRole and myRole of <partnerLink>s are manifested as service reference containers (<sref:service-ref>).

<sref:service-ref reference-scheme="URI">
content
</sref:service-ref>

Default is WS-Addressing endpoint reference:

<sref:service-ref>
<addr:EndpointReference>
<addr:Address>
http://example.com/auction/Registration/
</addr:Address>
<addr:ServiceName>
as:RegistrationService
</addr:ServiceName>
</addr:EndpointReference>
</sref:service-ref>

Variable Declaration

<variables>

Declare variables within a process or a scope. Variables hold XML data. Variable can be one of the following types: WSDL message type, XML Schema type, or XML Schema element. Variable is visible in the scope in which it is defined and in all nested scopes.

Syntax:

<variables>
<variable name="BPELVariableName"
messageType="QName"?
type="QName"?
element="QName"?>+
from-spec?
</variable>
</variables>

Example:

<variables>
<variable name="OrderForm"
messageType="ord:OrderFormMsg" />
</variables>

Manipulating Variables

<assign>

Update and copy data between variables, expressions, and partner link endpoint references.

<assign validate="yes|no"? standard-attributes>
standard-elements
<copy keepSrcElementName="yes|no"?
ignoreMissingFromData="yes|no"?>
from-spec
to-spec
</copy>
</assign>

<from variable="BPELVariableName" part="NCName"?>
<query queryLanguage="anyURI"?>?
queryContent
</query>
</from>
<from partnerLink="NCName"
endpointReference="myRole|partnerRole" />
<from variable="BPELVariableName"
property="QName" />
<from expressionLanguage="anyURI"?>
expression
</from>
<from>
<literal>literal value
</from>
<from/>

<to variable="BPELVariableName" part="NCName"?>
<query queryLanguage="anyURI"?>?
queryContent
</query>
</to>
<to partnerLink="NCName" />
<to variable="BPELVariableName"
property="QName" />
<to expressionLanguage="anyURI"?>
expression
</to>
<to/>

Example:

<assign>
<copy>
<from>$Order/Item/Amount * $ExchangeRate
<to>$OrderFrgn/Item/Amount
</copy>
</assign>

<validate>

Validates the values of variable against the associated XML or WSDL data definition. For invalid validation, bpel:invalidVariables fault is thrown.

<validate variables="BPELVariableNames" standard-attributes>
standard-elements
</validate>

Example:

<validate variables="Order OrderFrgn"/>

<sequence>

Defines a set of activities that will be executed in sequential order.

<sequence standard-attributes>
standard-elements
activity+
</sequence>

Example:

<sequence name="OrderProcessing">
<receive .../>
<assign>...</assign>
<invoke .../>
<reply .../>
</sequence>

<flow>

Specifies activities that should be performed concurrently.

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

Example:

<flow name="CheckPrice">
<invoke name="CheckSupl1" .../>
<invoke name="CheckSupl2" .../>
<invoke name="CheckSupl3" .../>
</flow>

To define synchronization dependencies between activities within <flow>, we use <links>. This way we define the order of execution. Links have to be declared within the <flow>.

Links: <targets> and <sources>

Define source and destination links for synchronization of flow activities. <source> is used to annotate an activity being a source of one or more links. <target> is used to annotate an activity being a target of one or more links. A link's target activity can be performed only after the source activity has been finished.

<targets>?
<joinCondition expressionLanguage="anyURI"?>?
bool-expr
</joinCondition>
<target linkName="NCName" />+
</targets>

<sources>?
<source linkName="NCName">+
<transitionCondition expressionLanguage="anyURI"?>?
bool-expr
</transitionCondition>
</source>
</sources>

Example:

<flow>
<links>
<link name="TravelStatusToTicketRequest" />
<link name="TicketRequestToTicketConfirmation" />
</links>
<assign>
<sources>
<source linkName="TravelStatusToTicketRequest" />
</sources>
<copy>...</copy>
</assign>
<invoke partnerLink="TicketConf" portType="tc:TicketPT"
operation="ConfirmTicket" inputVariable="TicketRequestVar"
outputVariable="TicektConfVar" >
<targets>
<target linkName="TravelStatusToTicketRequest" />
</targets>
<sources>
<source linkName="TicketRequestToTicketConfirmation" />
</sources>
</invoke>
...
</flow>

<joinCondition>

Defines explicit join condition for incoming (<target>) links. Default is OR (at least one incoming link to be true). Positive join condition (true) is required for starting the activity. If join condition evaluates to false, bpel:joinFailure fault is thrown (except if suppressJoinFailure="yes"). Example:

<targets>
<joinCondition>$TicketApproved and $DiscountGiven</joinCondition>
<target linkName="OrderTicket" />
<target linkName="IssuePayment" />
</targets>

<transitionCondition>

Defines the condition for outgoing (<source>) links to have positive status. Default is that they evaluate to true. Example:

<sources>
<source linkName="IssuePaymentAutomatic">
<transitionCondition>
$Ticket.Amount < 1000
</transitionCondition>
</source>
<source linkName=" IssuePaymentWithApproval">
<transitionCondition>
$Ticket.Amount >= 1000
</transitionCondition>
</source>
</sources>

suppressJoinFailure

Indicates whether a bpel:joinFailure fault should be suppressed or not. When not specified, it inherits its value from its closest enclosing construct.

suppressJoinFailure="yes|no"?

name

To give a name to the BPEL activity (not related with links).

name="NCName"?

<invoke>

Invokes an operation on a partner link web service.

<invoke partnerLink="NCName"
portType="QName"?
operation="NCName"
inputVariable="BPELVariableName"?
outputVariable="BPELVariableName"?
standard-attributes>
standard-elements
<correlations>?
<correlation set="NCName" initiate="yes|join|no"?
pattern="request|response|request-response"? />+
</correlations>
<catch faultName="QName"?
faultVariable="BPELVariableName"?
faultMessageType="QName"?
faultElement="QName"?>*
activity
</catch>
<catchAll>?
activity
</catchAll>
<compensationHandler>?
activity
</compensationHandler>
<toParts>?
<toPart part="NCName" fromVariable="BPELVariableName" />+
</toParts>
<fromParts>?
<fromPart part="NCName" toVariable="BPELVariableName" />+
</fromParts>
</invoke>

Example:

<invoke partnerLink="Ordering"
portType="ord:OrderPT"
operation="ConfirmOrder"
inputVariable="Order"
outputVariable="OrderConf" />

<receive>

Waits for an incoming message (operation invocation). Typical uses: first process activity (createInstance="yes"); to wait for callbacks.

<receive partnerLink="NCName"
portType="QName"?
operation="NCName"
variable="BPELVariableName"?
createInstance="yes|no"?
messageExchange="NCName"?
standard-attributes>
standard-elements
<correlations>?
<correlation set="NCName" initiate="yes|join|no"? />+
</correlations>
<fromParts>?
<fromPart part="NCName" toVariable="BPELVariableName" />+
</fromParts>
</receive>

Example:

<receive partnerLink="Ordering"
portType="ord:OrderCallbackPT"
operation="confirmOrder"
variable="OrderConfirmation"/>

<pick>

Waits for one of several possible messages (operation invocations) or for a time-out.

<pick> can be the first process activity (createInstance="yes", no <onAlarm> allowed).
<pick createInstance="yes|no"? standard-attributes>
standard-elements
<onMessage partnerLink="NCName"
portType="QName"?
operation="NCName"
variable="BPELVariableName"?
messageExchange="NCName"?>+
<correlations>?
<correlation set="NCName" initiate="yes|join|no"? />+
</correlations>
<fromParts>?
<fromPart part="NCName" toVariable="BPELVariableName" />+
</fromParts>
activity
</onMessage>
<onAlarm>*
(
<for expressionLanguage="anyURI"?>duration-expr</for>
|
<until expressionLanguage="anyURI"?>deadline-expr</until>
)
activity
</onAlarm>
</pick>

Example:

<pick>
<onMessage partnerLink="Ordering"
portType="ord:OrderPT"
operation="confirmOrder"
variable="OrderConfirmation">
...
</onMessage>
<onMessage partnerLink="Ordering"
portType="ord:OrderPT"
operation="cancelOrder"
variable="OrderCancelation">
...
</onMessage>
<onAlarm>
<for>'PT12H'</for>
<!-- Order completion timed out -->
</onAlarm>
</pick>

<reply>

Sends a response for a request-response operation (synchronous). The request is received using either <receive>, <onMessage>, or <onEvent>.

<reply partnerLink="NCName"
portType="QName"?
operation="NCName"
variable="BPELVariableName"?
faultName="QName"?
messageExchange="NCName"?
standard-attributes>
standard-elements
<correlations>?
<correlation set="NCName" initiate="yes|join|no"? />+
</correlations>
<toParts>?
<toPart part="NCName" fromVariable="BPELVariableName" />+
</toParts>
</reply>

Example:

<reply partnerLink="Ordering"
portType="ord:OrderPT"
operation="placeOrder"
variable="Order"/>

<wait>

Waits for a specified time period or until a certain deadline.

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

Example:

<wait>
<until>'2010-03-18T20:00+01:00'</until>
</wait>

<exit>

Immediately ends the BPEL process instance.

<exit standard-attributes>
standard-elements
</exit>

Example:

<exit/>

<empty>

This activity does not do anything. It is useful for synchronization of concurrent activities.

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

Example:

<empty/>

deadline-expr

Used in until expression of <onAlarm> and <wait>. XML Schema date or dateTime types are used to express deadlines (following ISO 8601).

<until>'2010-01-01'</until>
<until>'2010-03-18T21:00:00+01:00'</until>
<until>'18:05:30Z'</until>

duration-expr

Used in for expression of <onAlarm> and <wait>, and <repeatEvery> expression of <onAlarm>. XML Schema duration type is used (following ISO 8601).

<for>'PT4H10M'</for>
<for>'P1M3DT4H10M'</for>
<for>'P1Y11M14DT4H10M30S'</for>

<if>

To model decisions. <if> selects exactly one activity from the set of choices.

<if standard-attributes>
standard-elements
<condition expressionLanguage="anyURI"?>bool-expr</condition>
activity
<elseif>*
<condition expressionLanguage="anyURI"?>
bool-expr
</condition>
activity
</elseif>
<else>?
activity
</else>
</if>

Example:

<if>
<condition>
$Order.Amount > 1000
</condition>
... <!-- Make approval -->
<elseif>
<condition>
$Order.Amount >= 0
</condition>
... <!-- Process automatically -->
</elseif>
<else>
... <!-- Throw fault -->
</else>
</if>

<while>

Define a loop that repeats as long as the specified <condition> is true.

<while standard-attributes>
standard-elements
<condition expressionLanguage="anyURI"?>bool-expr</condition>
activity
</while>

Example:

<while>
<condition>$Order.Amount < 1000</condition>
<sequence>...</sequence>
</while>

<repeatUntil>

Defines a loop that repeats until the specified <condition> becomes true. The <condition> is tested after the loop activities complete. Loop will execute at least once.

<repeatUntil standard-attributes>
standard-elements
activity
<condition expressionLanguage="anyURI"?>bool-expr</condition>
</repeatUntil>

Example:

<repeatUntil>
<sequence>...</sequence>
<condition>$Order.Amount >= 1000</condition>
</repeatUntil>

<forEach>

Iterates its child scope activities in parallel (parallel="yes") or sequential manner, exactly <finalCounterValue>-<startCounterValue>+1 times. An optional <completionCondition> allows the <forEach> activity to complete without executing or finishing all the branches specified.

<forEach counterName="BPELVariableName" parallel="yes|no"
standard-attributes>
standard-elements
<startCounterValue expressionLanguage="anyURI"?>
unsigned-integer-expression
</startCounterValue>
<finalCounterValue expressionLanguage="anyURI"?>
unsigned-integer-expression
</finalCounterValue>
<completionCondition>?
<branches expressionLanguage="anyURI"?
successfulBranchesOnly="yes|no"?>
unsigned-integer-expression
</branches>
</completionCondition>
<scope ...>...</scope>
</forEach>

Example:

<forEach counterName="NoOfSuppliers" parallel="yes">
<startCounterValue>1</startCounterValue>
<finalCounterValue>3</finalCounterValue>
<scope>
<invoke name="CheckPrice" .../>
</scope>
</forEach>

<scope>

Defines a nested process scope with its own associated <partnerLinks>, <messageExchanges>, <variables>, <correlationSets>, <faultHandlers>, <compensationHandler>, <terminationHandler>, and <eventHandlers>.

<scope isolated="yes|no"? exitOnStandardFault="yes|no"?
standard-attributes>
standard-elements
<partnerLinks/>?
<messageExchanges/>?
<variables/>?
<correlationSets/>?
<faultHandlers/>?
<compensationHandler/>?
<terminationHandler/>?
<eventHandlers/>?
activity
</scope>

Example:

<scope name="CheckSupplier">
<partnerLinks>...</partnerLinks>
<variables>...</variables>
<faultHandlers>...</faultHandlers>
<sequence>
...
</sequence>
</scope>

<throw>

Generates a fault from inside the business process. Fault is identified by a qualified name.

<throw faultName="QName"
faultVariable="BPELVariableName"?
standard-attributes>
standard-elements
</throw>

Example:

<throw faultName="tns:InvalidOrder" />

<rethrow>

Rethrows the fault that was originally caught by the enclosing fault handler. <rethrow> can only be used within a fault handler (<catch> or <catchAll>).

<rethrow standard-attributes>
standard-elements
</rethrow>

Example:

<rethrow />

<faultHandlers>

Define the activities that are performed in response to faults. Fault handler can be <catch> or <catchAll>. They can be defined at the <process> level, within <scope>s, or inline for <invoke>.

<faultHandlers>?
<!-- There must be at least one faultHandler -->
<catch faultName="QName"?
faultVariable="BPELVariableName"?
( faultMessageType="QName" | faultElement="QName" )? >*
activity
</catch>
<catchAll>?
activity
</catchAll>
</faultHandlers>

Default fault handler:

<faultHandlers>
<catchAll>
<sequence>
<compensate />
<rethrow />
</sequence>
</catchAll>
</faultHandlers>

<eventHandlers>

Allow a process or scope to react on inbound messages (operation invocations) or on alarms. Event handler must contain at least one <onEvent> or <onAlarm> element. It can be defined at the <process> level or within <scope>s.

<eventHandlers>?
<!-- There must be at least one onEvent or onAlarm. -->
<onEvent partnerLink="NCName"
portType="QName"?
operation="NCName"
( messageType="QName" | element="QName" )?
variable="BPELVariableName"?
messageExchange="NCName"?>*
<correlations>?
<correlation set="NCName" initiate="yes|join|no"? />+
</correlations>
<fromParts>?
<fromPart part="NCName" toVariable="BPELVariableName" />+
</fromParts>
<scope ...>...</scope>
</onEvent>
<onAlarm>*
<!-- There must be at least one expression. -->
(
<for expressionLanguage="anyURI"?>duration-expr</for>
|
<until expressionLanguage="anyURI"?>deadline-expr</until>
)?
<repeatEvery expressionLanguage="anyURI"?>
duration-expr
</repeatEvery>?
<scope ...>...</scope>
</onAlarm>
</eventHandlers>

Example:

<eventHandlers>
<onEvent partnerLink="Ordering"
portType="ord:OrderPT"
operation="CancelOrder"
messageType="ord:CancelOrderMsg"
variable="CancelationDetails">
<scope>
...
</scope>
</onEvent>
<onAlarm>
<for>'PT12H'</for>
<scope>
...
</scope>
</onAlarm>
</eventHandlers>

<compensationHandler>

Defines activities that are processed for compensation. Can be defined within <scope> or inline for <invoke>.

<compensationHandler>
activity
</compensationHandler>

Default compensation handler:

<compensationHandler>
<compensate />
</compensationHandler>

<compensateScope>

Starts compensation on a specified inner scope that has already completed successfully. <compensateScope> can only be used within a fault handler, another compensation handler, or a termination handler.

<compensateScope target="NCName" standard-attributes>
standard-elements
</compensateScope>

Example:

<compensateScope target="PlaceOrder" />

<compensate>

Starts compensation on all inner scopes that have already completed successfully, in default order. <compensate> can only be used within a fault handler, another compensation handler, or a termination handler.

<compensate standard-attributes>
standard-elements
</compensate>

Example:

<compensate />

<terminationHandler>

Defines the activities that are performed when a BPEL process is force terminated. Can be defined within <scope>.

<terminationHandler>
activity
</terminationHandler>

Default compensation handler:

<terminationHandler>
<compensate />
</terminationHandler>

<messageExchanges>

Used to name message exchanges.

<messageExchanges>?
<messageExchange name="NCName" />+
</messageExchanges>

Default compensation handler:

<messageExchanges>
<messageExchange name="OrderME" />
</messageExchanges>

messageExchange attribute

Used to associate inbound message activities with <reply> activities (for example <receive> with <reply>). Use only if the execution can result in multiple pairs of inbound message activities and <reply>s.

object bpel:doXslTransform(string1, node-set, (string2, object)*)
string1 = style sheet name
node-set = source document for the transformation
string2 = XSLT parameter name
object = XSLT parameter value-can be XPath expression

Function returns the result of transformation. Example:

<assign>
<copy>
<from>bpel:doXslTransform("OrderXSLT.xsl", $Order)</from>
<to variable="OrderTransformed" />
</copy>
</assign>

<vprop:property>

Creates a unique name definition and associates it with an XML Schema type. <vprop:property> is defined in the service WSDL document, not in the BPEL.

<vprop:property name="NCName" type="QName"? element="QName"? />

Example:

<vprop:property name="OrderIDNumber" type="ord:OrdIDType" />

<vprop:propertyAlias>

Maps a property to a field in a specific message part or variable value. <vprop:property> is defined in the service WSDL document, not in the BPEL.

<vprop:propertyAlias propertyName="QName"
messageType="QName"? part="NCName"?
type="QName"?
element="QName"?>
<vprop:query queryLanguage="anyURI"?>?
queryContent
</vprop:query>
</vprop:propertyAlias>

Example:

<vprop:propertyAlias propertyName="tns:OrderIDNumber"
messageType="ord:OrderMsg" part="data">
<vprop:query>ord:OrderID</vprop:query>
</vprop:propertyAlias>

bpel:getVariableProperty()

Extracts property values from variables.

object bpel:getVariableProperty(string1, string2)
string1 - source variable name.
string2 - property to select from variable

Example:

bpel:getVariableProperty('Order','ord:OrderIDNumber')

<correlationSets>

Correlation set is a set of properties shared by all messages in the correlated group of operations within a process instance. Can be declared within a process or scope, or inline for <invoke>, <receive>, <reply>, <onMessage>, and <onEvent>.

<correlationSets>?
<correlationSet name="NCName" properties="QName-list" />+
</correlationSets>

Example:

<correlationSets>
<correlationSet name="Order"
properties="ord:OrderIDNumber ord:CustomerID" />
<correlationSet name="Invoice"
properties="ord:InvoiceNumber" />
</correlationSets>

<correlation>

Correlation can be used on <invoke>, <receive>, <reply>, <onMessage>, and <onEvent>. <correlation> indicates which correlation sets occur in the messages being sent and received. The initiate attribute is used to indicate whether the correlation set is being initiated (yes-initiated, join-initiated if not yet initiated, no-not initiated).

<correlations>
<correlation set="NCName"
initiate="yes|join|no"?
pattern="request|response|request-response"? />+
</correlations>

Example:

<receive partnerLink="Ordering" portType="ord:OrderPT"
operation="PurchaseRequest" variable="Order">
<correlations>
<correlation set="Order" initiate="yes" />
</correlations>
</receive>
...
<invoke partnerLink="Ordering" portType="ord:OrderPT"
operation="PurchaseResponse" inputVariable="OrderResponse">
<correlations>
<correlation set="Order" initiate="no" />
<correlation set="Invoice" initiate="yes" />
</correlations>
</invoke>